Implant abutment systems, devices, and techniques

ABSTRACT

Dental implant abutment systems, related devices, and implantology processes and techniques. The abutment systems include a base that is adapted to mount in nonrotating fashion on any desired dental implant, root form or blade, from any supplier, together with a fixation screw which secures the base to the implant. A core, to which an abutment is cast in customized shape and form as desired is attached to the base preferably in threaded fashion and secured with an appropriate antirotational mechanism. Alternatively, the core and abutment may be formed using CAM processes. Such abutment systems, unlike prevalent conventional systems, do not require a central access bore in the core or abutment components, and they occupy significantly less volume than conventional abutments. Accordingly, abutment systems according to the present invention more flexibly accommodate a wide range of axial inclinations between implant and the overlying crown or prosthesis, preclude loosening of fixation screws, allow precision attachments to be included in the abutments for providing virtually completely passively fitting patient removable prostheses, and save considerable time, effort and expense because of the added simplicity and lower parts inventory required. Also disclosed are tapered gingivectomy procedures for replicating natural tooth emergence which is enhanced by abutments according to the present invention, together with precision attachments, impression copings and analogs, and other peripheral components useful with systems and techniques of the present invention.

This application is a continuation of U.S. Ser. No. 09/130,335 entitled“Implant Abutment Systems, Devices and Techniques,” filed by Andrew J.M. Willoughby on Aug. 6, 1998, now U.S. Pat. No. 6,126,445, which is adivisional of U.S. Ser. No. 08/662,069 entitled “Implant AbutmentSystems, Devices and Techniques” filed by Andrew J. M. Willoughby onJun. 12, 1996, now U.S. Pat. No. 5,873,721, which is a divisional ofU.S. Ser. No. 08/176,011 entitled “Implant Abutment Systems, Devices andTechniques” filed by Andrew J. M. Willoughby on Dec. 23, 1993, now U.S.Pat. No. 5,527,182

The present invention relates to dental implant abutment systems,related devices, and implantology processes and techniques.

BACKGROUND OF TEE INVENTION

Various implant-related devices and systems have been created in recentyears in an effort to anchor dental prostheses more directly andflexibly in the mandible or maxilla than was possible using conventionaldentures or bridges. Conventional implant approaches have typicallyemployed a pre-manufactured coping or abutment which must be ground bythe practitioner or the lab in order to angulate the prosthesis whichrespect to the implant axis. Obviously, such angulation is limited insystems which require that the screw coupling the prosthesis to theimplant be inserted through a bore in the crown.

Such systems typically employ an anchor or “implant” which has beeninserted into the bone and from which extends prosthesis-supportingstructure typically coupled to the implant using a fixation screw orother desired fastener. All such systems have involved biologic andaesthetic compromises. Bacteria, food and other matter exacerbatecorrosion, chronic infection and bone loss. Secure fixation to theimplant often requires fasteners that extend from the crown and thusinvasion sites for foreign materials as well as distraction to thepatient. Conventional such systems also typically feature narrowemergence profiles from the gingival tissue (sometimes exposing metallicstructure) which can cause visually and often phonetically adverseaesthetic complications.

To the extent that conventional implant abutment systems employprecision attachments, they do so in a narrow manner, primarily tosecure prostheses such as bridges to copings on natural teeth or otheranchors. Such attachments have not been conventionally employed toprovide patient—removable prostheses, primarily because the abutmentdesigns (usually featuring a central access bore) could or did notaccommodate a precision attachment component within the contours of theabutment.

The following is a brief review of some of the conventional implant- andabutment-related references.

U.S. Pat. No. 5,116,225 issued to Riera (“Riera”) discloses an angulatedabutment system, a pair of bases which are adapted to fit together andwith the implant to allow prostheses to be disposed at a large number ofpredetermined angles with respect to the implant, a screw for mountingthe bases on the implant, and a two part abutment system which may bescrewed on the bases so that structures supporting the crown may bedisposed at various angles relative to the bases. The system thusapparently aims to provide great flexibility in lateral and verticalangulation of the prosthesis with respect to the implant. The Rierasystem allows for angulation correction in intervals as little as 6degrees by using a series of six different parts that are sequentiallyattached ending with a gold cylinder or plastic sheath that, once castor cast to, serves as the basis upon which the crown is to be built.This device features no means for preventing loosening of the fixationscrew, and it requires the laboratory to maintain comprehensiveinventories of plastic sheaths, cylinders and other angulatedcomponents. Furthermore, the components feature centrally disposedcylindrical bores which would impede inclusion of precision attachmentdevices for coupling crowns or other devices.

U.S. Pat. No. 5,106,299 issued to Ghalili (“Ghalili”) discloses a dentalimplant system which includes an abutment adapted to connect to upperportions of an implant, held in place using a fixation screw, and upperportions of which are adapted to receive an insert which bears againstthe fixation screw and a spring loaded device to hold the insert inplace so that the fixation screw does not loosen. The crown fits theabutment. The Ghalili abutment, because of its height, permitsrelatively little angulation of the crown from the implant axis.Furthermore, the central bore of the abutment would interfere withprecision attachments or other connection devices for prostheses orcrowns. Additionally, the Ghalili anti-rotational pin is exposed on theexterior of the crown, which can introduce hygiene problems,particularly when combined with the relatively complex spring-loadedmechanism of the pin.

U.S. Pat. No. 5,125,839 issued to Ingber (“Ingber”) discloses an implantsystem that includes an abutment held in place on an implant via afixation screw, and to which a crown may be attached. The fixation screwenters through the top of the crown, which may be filled using resinfiller. The Ingber implant assembly, while it facilitates customizedformation and fitting of dental prostheses, requires a central bore inthe crown for the fixation screw which requires a dental filler and thusimpedes aesthetic effects, durability, retrievability, and does notadequately address the issues of screw loosening. Additionally, therequirement of a central bore in the crown to accommodate the fixationscrew dramatically limits angulation of the crown with respect l.o theimplant axis.

U.S. Pat. No. 5,104,318 issued to Peshe (“Peshe”) once again disclosesan implant system which includes an abutment adapted for connection toan implant, with fixation screw for connecting the abutment to theimplant, and a separate retainer screw for attaching the crown to thefixation screw and the abutment. The Peshe structure, with itsconceptually similar fixation screw and abutment, together with crownbore, presents the same types of problems as Ingber.

U.S. Pat. Nos. 4,854,872 and 5,015,186 issued to Detsch (respectively,“Detsch 872” and “Detsch 186”) disclose prosthetic implant attachmentsystems that include a base member having a lower end adapted to seat onthe upper end of the implant, and an upper end of diameter correspondingto profiles of various teeth, a securing device for securing the base tothe implant, and various straight and angled or variably angledprosthetic heads attached to the base for supporting the crown. TheDetsch 186 attachment system once again features a crown with acentrally disposed bore through which a fixation screw must attach, withthe concomitant flexibility, durability, aesthetic problems and screwloosening problems.

U.S. Pat. No. 4,713,003 issued to Symington et al. (“Symington”)discloses a device for attaching a prosthesis to an implant. The deviceincludes a fixation screw for insertion in the implant which in turncarries an abutment connected to the fixation screw by a second screw.The abutment may carry a prosthesis, and it may also attach to aprosthesis via a retaining screw received in a threaded cavity in upperportions of the abutment. The Symington system once again requires acentrally oriented bore in the crown.

U.S. Pat. No. 4,780,080 issued to Haris (“Haris”) discloses an implantsystem formed of a root member implanted in the bone and carrying a postin which an angular stewed head may be mounted for supporting a crown.The Haris system relies heavily on dental cement and fails to controlrotation of the base with respect to the implant.

U.S. Pat. No. 4,988,298 issued to Lazzara (“Lazzara 298”) discloses adental implant system that contains a precision machined abutment forattachment to an implant and which supports a crown, portions of whichare attached to the abutment. U.S. Pat. No. 4,955,811 issued to Lazzara(“Lazzara 811”) discloses a dental implant fixture that is non-rotatablyconnected to an implant and includes a two part impression coping thatmay be non-rotatably connected to the implant. U.S. Pat. No. 4,850,870issued to Lazzara et al (“Lazzara 870”) discloses various abutment postsand copings for use with implants. U.S. Pat. No. 4,856,994 issued toLazzara et al (“Lazzara 994”) discloses a healing cap for use in dentalimplantology during healing in gingival tissue. The Lazzara systems arestate of the art, but their premanufactured nature impairs flexibilityin conforming an abutment and a prosthesis to the gingiva in a mannerand at proper angulation to replicate the look and feel of naturalteeth.

U.S. Pat. No. 4,318,696 issued to Kasama (“Kasama”) discloses an implantsystem featuring elastic material attached to the head of the implant,together with a crown attached to the elastic material. U.S. Pat. No.5,033,962 issued to Scatena (“Scatena”) discloses an implant system thatincludes a “stump” which features a lower part or base for connection toan implant, and an upper head which attaches to a cap via an elasticelement. The cap supports a crown. The Kasama device correctly addressesthe need in certain cases to replicate natural root/ligament-inducedarticulation in opposing elastic or flexible material between the crownand the implant. The Scatena device also includes an elastic element,but between a cap which supports the crown and a head which fits theimplant. However, the Scatena structure appears to include no mechanismfor preventing rotation between the head and the implant, and theelastic material is distanced from the bone.

U.S. Pat. Nos. 5,073,111, 5,035,619, and 5,145,372, issued to Daftary(respectively “Daftary 111”, “Daftary 619” and “Daftary 372”) disclose asystem and method for implanting tooth analogues which include astandard implant and a cover screw which may be replaced with a healingcap for healing of the gingival tissue. The healing cap may then beremoved and replaced by an abutment having an emergence profile matchingthat of the healing cap, which abutment is adapted to receive a crown.The Daftary 111 patent healing cap claims to provide frusto conicalemergence profile in the gingival tissue more closely simulating that ofa natural tooth. It unfortunately provides only a circular cross sectiongingival cuff, however, and various healing caps of various heights mustbe inventoried in order to accommodate differing gum thicknesses anddesired emergence profile.

SUMMARY OF THE INVENTION

The present invention provides a universal abutment system (and relateddevices, components and processes and techniques) which includes a basethat is adapted to mount in non-rotating fashion on any desired dentalimplant, together with a fixation screw, which secures the base to theimplant. A core, to which the abutment may be cast as desired from anappropriate wax-up, is attached to the base (preferably) in threadedfashion and secured with an appropriate anti-rotational mechanism suchas an anti-locking screw, sliding lock or other suitable device.

The core and abutment of devices according to the present invention,unlike the prevalent conventional systems, do not require a central borein the core component for insertion of the base/implant fixation screw.That significant and distinct feature, plus the relatively small size ofthe core, provides essentially an open palate for fashioning wax-ups andcasting abutments of any desired shape, profile, shape and angulation inorder to accommodate naturally occurring tooth profiles. The core,abutment and crown provide prostheses that have the same shape as actualand wax-up teeth both in their exposed and transmucosal portions, foraesthetic and accessibility reasons. Since teeth obviously came in manydifferent sizes and shapes, each wax-up must be customized. Thiscustomized capability is not possible with other conventionallypremanufactured systems.

Accordingly, the universal abutments according to the present inventionpermit unlimited vertical and horizontal angulation, and they eliminateany compromise of fixation screw, base or abutment strength caused inprevious designs by grinding or heating. The shorter base/implantfixation screw receives less bending movement due to the base/implantsurrounding connection and shortened length of the fixation screwrelative to the previous design. The system additionally may be easilydisassembled and retrieved with no requirement for dental cement.Previous inventory requirements for large numbers of parts toaccommodate various prosthesis/implant angulations are no longerdesired. The additional flexibility allows greater latitude in selectingemergence of a screw block that connects the crown to the abutment,which now may be located more easily in the cingulum area of the crown.

Abutment systems according to the present design also allow intracoronalprecision locking attachment components to be placed in the abutment,which can accommodate corresponding attachment components fixed in theinterior portions of a bridge, overdenture or other prosthesis in orderto allow the prosthesis easily to be removed and cleaned at will. Theprecision locking attachments may be aligned on the abutments nearer theimplant axis (and the abutments aligned) more easily because no centralabutment bore for the fixation screw need be accommodated; the bridgemay thus smoothly and passively fit to the abutments. In implementationsusing a combination of implants and natural teeth, the abutments maycontain a resilient core to replicate root/ligament articulation andthus consistent articulation of the prosthesis.

The core and base may be prepared locally via computer aided machining.Computer aided manufacturing devices such as those presently used forcrown fabrication may be controlled via data obtained from visual orother appropriate scanning of the mouth in order to mill blanks oftitanium or other appropriate material in which appropriate threads,orifices, shoulders and other features have been pro-precision machinedto accommodate the base and anti-rotational mechanism and the precisetolerances of these features required in the present system.

The implantology processes employing these systems is radicallydifferent from previous such processes. Very briefly, as discussed indetail below, a first model and first or surgical template are created,and the implants are placed in the mouth to be incorporated in the bonestructure for a several month (typically) healing period, as inconventional processes. A second stone model is created with outimplants in place and accurate wax-ups are created on this second model.Full anatomical contours of the wax-ups are noted on the model. Theircontours are outlined in pencil, the wax-ups are carefully removed, anda clear template is drawn down over the pencilled outline. This secondtemplate is cut to correspond to a smaller set of second outlines asdisclosed further below. The template is additionally contoured using anangle burr to replicate natural tooth emergence from the gingiva. This“Tapered Gingivectomy Template” is employed to excise gingival tissue inthe vicinity of the implant in order to create a tapered gingival cuffsimulating a natural emergence profile, and through which the base,core, abutment and crown may extend.

Healing collars are fashioned for the (non-circular profile) gingivalcuffs using wax-ups so that the gingival tissue heals corresponding tothe desired emergence profile. Appropriate abutments and crowns arecreated on models all as disclosed in further detail below to beinstalled in a manner that closely replicates the look and feel ofnatural teeth.

These systems, devices and techniques are well suited for, among otherapplications, patient removable bridges, overdentures, other prosthesesand virtually any implant-based dental restoration.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 in a perspective view of a dental model showing a number ofcomponents according to the present invention, including a UniversalAbutment System (“UAS”) assembly, a Universal Abutment Systemimplant-base-core assembly, a temporary that includes a Locking HealingCollar to which a temporary abutment has been cast, and a LockingHealing Collar.

FIG. 2 is an exploded cross sectional view of a UAS assembly accordingto the present invention.

FIG. 3 is a cross sectional view showing the UAS assembly of FIG. 2after placement.

FIG. 4 is an exploded cross sectional view of a UAS assembly accordingto the present invention whose interlock structure with the implantdiffers from that of the assembly shown in FIG. 2.

FIG. 5 is a cross sectional view showing the UAS assembly of FIG. 4after placement.

FIG. 6 is a cross sectional view showing a Resilient Core UAS assemblyaccording to the present invention after placement.

FIG. 7 is an exploded perspective view showing a UAS threaded base andcore according to the present invention which employ a sliding lockrather than a locking screw for preventing rotation of the core relativeto the base.

FIG. 8 is an exploded perspective view showing the components of FIG. 7and with an abutment formed on the core.

FIG. 9 is perspective view showing the components of FIG. 8 beingfurther assembled.

FIG. 10 is a perspective view showing the components of FIG. 9 in place.

FIG. 11 is a perspective view showing the components of FIG. 10 beingfit with a crown.

FIG. 12 is a perspective view of components of a Milled UniversalAbutment System (“MUAS”) according to the present invention.

FIG. 13 is a perspective view of components of a MUAS which includes aresilient core.

FIG. 14 is a perspective view of a blank which may be used to mill aMUAS.

FIG. 15 is a perspective view of the blank of FIG. 14 from an upperaspect.

FIG. 16 is a schematic view of a computer aided design device which maybe used to design and prepare a MUAS.

FIG. 16A is a schematic view which shows an abutment contour in anactual blank corresponding to the image on the screenface of FIG. 16.

FIG. 17 is a schematic block diagram of a CAD/CAM system which may beemployed to design and prepare a MUAS.

FIG. 18 is a perspective view of a MUAS blank that employs a slidinglock rather than a locking screw.

FIG. 19 is a perspective view of a second embodiment of a MUAS blankthat employs a sliding lock rather than a locking screw.

FIG. 20 is a perspective view of a third embodiment of a MUAS blank thatemploys a sliding lock rather than a locking screw, which includes aresilient core.

FIG. 21 is a schematic view of a blank according to FIG. 19 with thecontour of a desired abutment.

FIG. 22 is a schematic view of the blank of FIG. 21 partiallydisassembled.

FIG. 23 is a perspective view of a stone model on which wax up contoursare being outlined in accordance with Tapered Gingivectomy proceduresaccording to the present invention.

FIG. 24 is a perspective view showing a Tapered Gingivectomy Templateused in Tapered Gingivectomy procedures according to the presentinvention.

FIG. 25A is an exploded cross sectional view of a Modified Impressioncoping according to the present invention.

FIG. 25B is a cross sectional view of the coping of FIG. 25A beingsyringed with material to form an impression.

FIG. 26A is an exploded cross sectional view of a Flexible ModifiedImpression Coping according to the present invention.

FIG. 26B is a cross sectional view of the Flexible Modified ImpressionCoping of FIG. 26A being syringed with material to form an impression.

FIG. 27A is a cross sectional view of a Modified Implant Analogaccording to the present invention.

FIG. 27B is a cross sectional view of the Modified Implant Analog ofFIG. 27A attached to a Flexible Modified Impression Coping.

FIG. 28 is an exploded perspective view of a UAS fitted with a precisionattachment according to the present invention.

FIG. 29 is a cross sectional view of the UAS of FIG. 28 that has beenplaced.

FIG. 30 is an exploded perspective view of a UAS according to thepresent invention for use in a stress broken denture according to thepresent invention.

FIG. 30A is an exploded perspective view of a precision attachmentaccording to the present invention for use in a stress broken dentureaccording to the present invention.

FIG. 30B is a cross sectional view of a matrix analog, patrix analog,matrix, patrix and INS spacer according to the present invention.

FIG. 31 is an exploded perspective view of a Vertex precision attachmentaccording to the present invention.

FIG. 32 is an exploded cross sectional view of Vertex precisionattachments employed for retention of a passive fitting prosthesisaccording to the present invention.

FIG. 33 is a cross sectional view of a prosthesis which employsconventional precision attachments and implant abutment systems thatutilize an intra-mobile element.

FIG. 34, by comparison, is a cross sectional view of a prosthesissimilar to that of FIG. 33, but which employs precision attachments andan implant abutment according to the present invention (in the form of amodified Uniform Abutment System which employs a resilient core).

FIG. 35 is a cross sectional view of an overdenture which employsconventional precision attachments and implant abutment systems.

FIG. 36, by comparison, is a cross sectional view of an overdenturesimilar to that of FIG. 35, but which employs precision attachments andan implant abutment according to the present invention.

FIG. 37 is a perspective view of a conventional blade implant that hasbeen modified to accommodate components of the present invention.

FIG. 38 is a cross sectional view of the implant of FIG. 37 supportingabutment components of the present invention.

FIGS. 39A and 39B, 40A and 40B are schematic diagrams showing steps in asplit frame index process according to the present invention.

DETAILED DESCRIPTION Section I: Contest: Reevaluating Progressive BoneLoading

Context Part 1: Progressive Bone Loading And the Issue of Stage IIUncovery.

The majority of root form endosteal implant literature suggests thatimplant mobility is directly related to the anatomic location of theimplant during the first year of prosthetic loading. Implant mobility isalso related to bone density, implant size, surgical approach andpremature loading of the implant prosthesis. The ratio of theprosthesis' height and width to the implant length is another importantfactor. New techniques of progressively bone loading an edentulousspace, especially a full arch are, however, necessary to address morecompletely the issue of implant mobility and longevity.

This Section I discloses new techniques for progressive bone loading inthe edentulous arch which employ a more accurate manner of registering,verifying and transferring the vertical dimension, centric relationocclusion and anterior guidance from the temporary prosthesis to thepermanent prosthesis. This is achieved by using UAS according to thepresent invention as disclosed further below in Section III and MUAS inSection V. This Section also addresses the effect of elevating theperiosteum at state II uncovery on the ability of the bone to recoverfrom premature occlusal loading.

Also addressed is the issue of bone maturation and premature occlusalloading. According to Wolff's law, trabecular bone places and displacesitself relative to the forces to which it is subjected. Therefore, theprogressive bone loading of endosteal implants is an accepted protocolbecause it allows immature woven bone (often present at the implant-boneinterface upon placement) to be slowly replaced with a more denseload-bearing lamellar bone. It is the presence of this denser lamellarbone and an increase in the amount of bone at the implant-bone interfacethat reduces the amount of implant mobility, especially during the firstyear of implant placement. In fact, complete bone maturation requirestwelve to eighteen months from the time of initial placement and this isall the more reason why the wear time of the interim prosthesis shouldbe extended.

Unfortunately for many patients, the clinician often races to see howquickly and with how few appointments the permanent prosthesis can bedelivered. For example, the average full arch implant case is restored2-3 months after recovery and in as little as 6 or 7 appointments. Thispractice is likely, however, to lead to detrimental long-term effects,not only on the implant-bone interface, but also on the patient'stemporomandibular joints and surrounding musculature.

In order to make better sense of the following technology and these newtechniques, this Section progresses through a hypothetical case; it alsodiscloses an alternative method of rehabilitating the patient'socclusion using this technology.

A new technique has also been developed to prevent the unnecessary lossof peri-implant bone as the result of a Stage II full periosteal flap.The technique involves the use of a tapered gingivectomy procedure thatnot only offers a less invasive method of implant uncovery but alsooffers the means to create fully anatomically contoured soft tissueemergence profiles. The effects of this technique are obviouslybeneficial: Elimination of the need to disturb the periosteum means thatthe tissue heals faster, the underlying bone is not deprived of itsblood supply and therefore the bone remains healthy and can be loadedsooner. Moreover, prosthetics can be contoured more accurately andreadily to resemble natural tooth contours.

The key to progressive bone loading is to allow for a controlled loadingof the implant-bone interface. This cannot be done if the clinician ispeeling back the periosteum to expose the implants and place healingcollars, for the act of peeling the periosteum off of the bone leads toa decreased blood supply. It takes many months before the periosteumreheals and its blood supply to the underlying bone is completelyregenerated. If during this healing phase the implants are prematurelyloaded, the surrounding bone is unable to absorb the occlusal forcesbecause it is not receiving an adequately nutrient-rich blood supply.This leads to microfracting of bone, osteoclastic activity, corticalcratering and even a vascular necrosis which appears clinically as boneloss, cupping of bone around the neck of the implant and even mobilityin extreme cases. Avoidance of flapping of the periosteum and a slowermore controlled progressive loading of the implant could induce morepredictable clinical results and loss bone loss. Furthermore, properprogressive bone loading allows more time to be spent developing theappropriate occlusal scheme and because a split frame index can beutilized for this purpose, the patients' occlusion can be moreaccurately recorded and reproduced in the final prosthesis.

The Steps in Progressive Bone Loading

With the technology of the present invention progressive bone loadingcan begin shortly after implant uncovery because the periosteum isusually not elevated.

The first commonly accepted step in progressive bone-loading is theplacement of healing collars which allow for soft tissue healing,formation of the transmucosal cuff and occlusal loading.

In situations where the prosthesis is to be fixed into the patient'smouth, a tapered gingivectomy is required (see Section IV) and thereforethe healing collars must be customized. In the fully edentuloussituation the prosthesis can be made patient precision attachmentremovable and so healing collars with tapered transmucosal cuffs are notrequired. In either situation healing collars must be placed but shouldnot be directly loaded by any prosthesis for the first few weeks. Thistime period can, however, vary quite significantly.

When the healing collar is placed, the periosteum is not elevated, andtissue healing will take only 2-3 weeks; if the periosteum is elevated,healing will take 6-8 weeks. Therefore, if for no other reason than thetime factor, every effort should be made not to elevate the periosteumat the time of implant uncovery.

However, many clinical cases are lose than ideal. For example, whentissue guided regeneration procedures are used to augment bone aroundthe implant, bone can grow right over the top of the implant cover screwduring integration. The result is often difficult access for the tissuepunch. In this situation a conservative internal flap design may beindicated to gain sufficient access in order to remove the necessarybone. If this procedure is required, the periosteum must be allowed toheal completely (which takes 6-8 weeks) before the tapered gingivectomyis performed and the healing collar is placed. It is absolutelyimperative that the implant-bone interface not be loaded for this 6-8week period if the periosteum has been disturbed.

It has been said that the healing cap should seal and be of the samediameter as the outer part of the implant to prevent soft tissueingrowth. Unfortunately, this frequently leads to the formation of astandard straight transmucosal cuff. It is the inventor's belief,however, that the transmucosal cuff should be surgically tapered andthen further modified by both the healing collar and the final abutmentto create a completely customized tapered transmucosal cuff in all butthe patient removable situations. This procedure provides a way ofaccurately creating natural anatomically correct soft tissue emergenceprofiles for the overlying prosthesis. This, in turn, allows theprosthesis to be contoured in such a way that it too reflects theanatomical shape of the natural teeth. Up until now, there have onlybeen a limited number of ways in which to create fully contoured crowns.This usually involved overexpanding and crushing the tissue,ridgelapping or by using symmetrical tapered healing abutments.overexpanding the tissue without first surgically tapering it accordingto the present invention creates gingival clefting, sloughing of tissueand recession. Ridgelapping causes plaque accumulation leading to periimplantitis and the frusto-conically shaped tapered healing abutmentsfrom some companies require periosteal elevation and create symmetricalsoft tissue profiles. As will be seen in more detail later, in order tocreate more anatomically correct soft tissue contours without elevatingthe periosteum, crushing the tissue or ridgelapping, an accuratesurgical template is needed to first carry out the tapered transmicosalgingivectomy. Then, the healing collar must have a custom taperedcapability in order to expand the tissue slightly and hold the tissue toits correct shape during healing. These two components are sometimesreferred to herein as a gingivectomy template and a custom lockinghealing collar.

The tapered peri-implant sulcus or transmucosal cuff can also bemodified by the final prosthesis as well; therefore, an abutment thatcan be flared and customized in terms of its emergence profile must beused. Conventional UCLA abutments cannot be used to create this flare,because, as discussed below, they cannot overcome the screw looseningand central access bore problems. With the universal abutment systems ofthe present invention (sometimes hereinafter, “UAS”), which maintainexact tissue contour, these problems have been eliminated. Advantages ofthese systems include: (1) hygienic access; (2) better aesthetics; (3)natural crown contours to help eliminate phonetic problems and foodimpaction and (4) an anti screw loosening capability. The systems aredescribed further in Sections III, IV and V.

In the edentulous jaw, tapered transmucosal cuffs are not necessary tocreate hygienic access because of new and innovative removable precisionattachment prostheses according to the present invention which allow thepatient to remove crown and bridge appliances and expose the individualabutments for periodontal cleaning. In order to illustrate the newprinciples of design and technique, consider an edentulous maxillaopposed by a partially edentulous mandible when four implants replacethe missing lower molar teeth and six implants are present in the upperjaw. With existing systems it is common practice at the secondappointment (3-4 weeks after flapping the tissue) to replace the healingcaps with the abutment of final size and height. However, this is fartoo premature because even though the gingival tissue around the healingcollar may have healed, the underlying periosteum has not (not for atleast another 3-4 weeks). Therefore, if a clinician chooses to use thisstandard technique, all that should in fact be done at this secondappointment is to take an analog transfer impression in order to preventdamaging the periosteum.

With modified impression copings according to the present invention asdisclosed below, the analog transfer impression can be accomplished atthe first visit because the periosteum has not been elevated. Asdiscussed in Section IV below, modified implant analogs can be attachedto these modified impression copings so that they not only provide animplant analog transfer which duplicates the precise axial androtational position of the implant, but they can also be used innon-patient removable cases to capture the tapered gingivectomy contoursin the same impression. This can all be accomplished at the firstappointment which also allows the temporary to rest more sturdily on thelocking healing collars after an appropriate period of initial healing.Most importantly this can be achieved without elevating the periosteum.

It is also important to remember that the locking healing collarsaccording to the present invention have the ability to be lab alteredand individually customized. In the edentulous situation it is notnecessary to incorporate a tapered transmucosal component because theoverlying prosthesis, even though it is ridgelapped and overcontoured,can now be made patient removable for hygienic access according to thepresent invention. Furthermore, locking healing collars of the presentinvention are less likely to loosen than the standard screw-in healingcollar because of their design which prevents soft tissue impingementbetween the superior edge of the implant and the base of the healingcollar. This is a very common problem with existing healing collarswhich plagues clinicians and causes them routinely to performunnecessary and avoidable gingivectomy procedures in order to removeexcess tissue tags.

With conventional systems, usually only 1-4 weeks is required before thethird appointment. At this stage most clinicians undertake theprosthetic reconstruction of the edentulous arch. The inventor believesthis is far too soon, using existing techniques, because not only hasthe periosteum barely had time to heal completely (by this point amaximum of seven weeks will have passed since uncovery), but theinventor also believes that insufficient attention has been given toestablishing the temporary occlusion and bone loading the implant-boneinterface. Why do some consider the occlusion in the permanentprosthesis so critical and not the temporary? After all, how stable is adenture occlusion if it is anchored to a non-passive fitting tissue barand a softlined denture, especially if the reconstruction is beingrushed and has been placed on top of freshly elevated periosteum?Perhaps these are some of the reasons behind unexplained implant loss.Approaches of the present invention to full arch implant reconstruction,by contrast, permit initial reconstruction of a stable interimprosthesis after the first appointment without elevating the periosteum.The reconstruction takes several appointments to complete and is thenleft in place for a minimum of 3-4 months to progressively bone load theimplant bone interface.

In an edentulous situation when the clinician is reestablishing thecentric relation at the correct vertical dimension of occlusion (centricrelation occlusion) and with all the appropriate centric and eccentriccontacts, their accurate registration cannot be established by standardaesthetic and occlusal try-in procedures. In fact, unless the interimprosthesis can provide a stable reproducible set of registrations theclinician is unwittingly and arbitrarily setting the occlusal patternfor the final prosthesis. This can have profound long-term effects onthe surrounding musculature and TM joints. It is not enough simply totake “occlusal try-in records” and then have a metal frameworkfabricated while adjusting the temporaries and placing them intoocclusion. There must be a way of verifying that the final prosthesisaccurately duplicates the same occlusal determinants as established bythe interim denture. The interim denture cannot simply be removed andthen the framework tied in because then all the centric stops are lost,and the clinician is left “lost at sea”.

As stated earlier, many clinicians feel that 1-4 weeks after occlusallyloading the temporary, the patient can receive the final implantsupported prosthesis. The inventor believes that this seems an awfullylarge leap of faith; after all, one wonders whether this is really longenough to leave a temporary prosthesis before determining whether the TMjoints musculature and occlusion are stable and asymptomatic, not tomention whether or not aesthetic and hygienic concerns are being met orwhether the implant-bone interface circulation has totally rehealed. Ifthese concerns are not being adequately addressed then how can aso-called permanent prosthesis be created? Do not forget that in thepartially edentulous or single tooth situation where there arepreexisting stable centric stops, establishing a CRO position andprogressively bone loading the implants is not as complicated, simplybecause the patient's natural dentition can be utilized.

Context Part 2: Using an Interim Denture and a Split Frame Index: A NewTechnique for Accurately Registering, Verifying and Transferring anMentulous Patient's Occolusal Determinants.

A split frame index technique has been developed according to thepresent invention in conjunction with a unique interim denture in orderto (a) control the progressive bone loading of the integrated implant,and (b) aid in accurately registering, transferring and verifyingcentric relation, anterior guidance and vertical dimension of occlusionin an edentulous patient. FIGS. 39 and 40 (39A and B, 40A and B)schematically show steps in the process. The use of precisionattachments mounted within the normal abutment contours of the presentinvention allows very accurate positioning and repositioning of theinterim prosthesis. The split frame index technique utilizes one-half ofthe interim denture in order to hold the bite while the left half andthen the right half of the final precision attachment framework (alsopart of the present invention) is used to record, transfer and verifythe correct occlusal positions.

In the full arch situation, the interim denture fabrication can begin atthe first appointment (the implant uncovery appointments with a try-inof the stabilized acrylic bases loosely fitted over top of lockinghealing collars in the mouth. These stabilized bases are modified atthis first appointment to fit down over the lubricated sleeves of thelocking healing collars. The sleeves are made of plastic according tothe present invention and can be adjusted for draw (path of insertion).Acrylic can be flowed around the sleeves of these healing collars toincrease the fit and stability of the bases.

This provides the same type of passive fit that the conventional KALtechnique claims in a permanent prosthesis, but because they both havethe same problems with screw loosening, this approach provides a morethan adequate temporary solution but certainly not one that can becarried over into the permanent fixture. While the interim denture isbeing fabricated, the patient uses their old denture which is secured tothe locking healing collars with a soft liner.

Occlusal rims can be fabricated using greystick compound and by applyingneutral gone principles. Centric relation occlusion is registered in theedentulous case by an inter-occlusal centric relation bite record. Afacebow transfer record could then be taken to help mount the casts.Tongue and cheek matrices can be taken and trimmed back to the exactheight of the occlusal plane. This is all done at the secondappointment. The accuracy of the mounting should then be verified byusing a separated cast technique. Upper anterior teeth can then be setin accordance with anterior guidance principles for the naturaldentition, even though they may be modified at a later date toredistribute the occlusal load.

The interim anterior set up is tried in at the third appointment and adetermination of the precise upper incisal edge location is made. Theanterior teeth can then be set more firmly in acrylic which requires anadditional lab procedure involving fabrication of a matrix. only afterthis has been done can all excursive pathways from centric relation toan edge to edge relationship be check and adjusted. At this next(fourth) appointment an adjustment for long centric can also be made. Acentric occlusal bite record should also be taken in the posteriorsegments at the correct vertical dimension (determined by solid anteriortooth contact) and then the anterior try-in denture can be remounted onthe articulator. The patient's old relined dentures are re-inserted andthe patient is instructed to remain on a soft diet. Before the fifthappointment and only if all anterior guidance contours are definite canthe clinician finish restoring the lower posterior teeth.

The use of a Broadrick Occlusal Plane Analyzer is helpful in setting anideal curve of Spee and curve of Wilson. At this point the position ofboth the buccal and lingual cusp tips and their appropriate contoursshould be determined. This can be done by fabricating acrylictemporaries on top of universal abutment systems of the presentinvention and grinding of the lower buccal cusp tips to match the exactline and plane of occlusion. The upper posterior teeth can now be set onthe interim denture using 30° inclined plane denture teeth so that onlythe lingual cusp tips engage the lower fossae. At this stage, both thelingual cusp tips and the fossae contours of the lowers may have to bealtered as well. A narrow occlusal table should be created to helpreduce damaging lateral stresses and occlusal forces. At this time thepatient may be brought in for another try-in.

At the sixth appointment, the lower posterior implant supportedtemporaries can be cemented in and the maxillary interim denture can betried in. When the try-in is acceptable, the interim denture isprocessed and new tongue and cheek matrices of the interim denture aremounted on the working models and finalized contours can be set for theUAS abutments. Careful attention is paid to allowing sufficientclearance for the framework and crowns that fit overtop of theabutments. Precision attachment housings are then resin-bonded intoplace in the appropriate implant abutments of the present inventionaccording to resin bonding techniques of the present invention. Once theprocessed interim denture has been remounted on the articulator, itsunderside can be hollowed out so that the implant abutments can beproperly positioned without interfering with the denture. This hollowedout space is created around each abutment so that when patrix analogcomponents according to the present invention are inserted into femalematrices, acrylic can be flowed into the denture and around the patrixanalog flags. In order to assure a passive fit, this procedure should bedone intraorally. Once the acrylic has set, the interim denture can bedetached from the patient's mouth.

This assembly is not only patient removable but it also provides a veryaccurate and very stable interim denture. This is a tremendous help whentrying to duplicate in the mouth the same occlusal markings created onthe articulator. This usually means that the denture is created with abilaterally balanced occlusion and no excursive interferences. When theclinician is satisfied with the aesthetics and occlusal patterns.impressions can be taken off both arches and the models remounted forlater comparison.

The patient should be left in the interim prosthesis for 3-4 months toallow for adequate bone maturation around the implants and occlusalanalysis. The patient should also be reminded to maintain a soft dietand instructed on how to remove the interim denture and clean around theabutments. A rotadent or a hydrofloss machine is ideally suited for thispurpose.

By the fifth appointment, most clinicians have already delivered thefinal prosthesis. However, the inventor believes they have done so by(1) arbitrarily setting many of the patients' occlusal determinants, and(2) rushing the progressive bone loading. Therefore, the long-termhealth and stability of the patients' gnathostomatic system isquestionable.

On the other hand, with the implant supported precision attachmentinterim dentures according to the present invention, everything is madeto be stable and reproducible before the definitive prosthesis isfabricated, which gives the patient 3-4 more months of progressive boneloading. After this maturation phase is over, if the patient's TM jointsand surrounding musculature are comfortable and pain-free, and theaesthetics and phonetics are acceptable, a final set of records is takento mount the interim denture and the abutment back onto the articulatorand the patient is given their old denture which is anchored to place bythe locking healing collars. Then, and only then, can the finalprosthesis be fabricated.

The inventor, as well as other notable clinicians such as Dr. PeterDawson, believes that stable reproducible records cannot be transferredaccurately from the interim denture to the final prosthesis withoutbeing verified intra-orally. The only effective way to accomplish thisfor the edentulous implant patient is by using a technique referred toherein as the “split frame indexing technique.” This technique isemployed to help determine and verify anterior tooth position at thecorrect vertical dimension. Dawson states that “anterior guidance is apropix determinant of posterior occlusal form” (P. E. Dawson,Evaluation, Diagnosis and Treatment of Occlusal Problems ch. 16 (C.V.Mosby Co. 2d ed. 1989) and the inventor believes that with the splitframe index the appropriate posterior occlusal contacts can beaccurately produced, once the anterior guidance has been established.

Split frame indexing is a technique that has been developed in order toensure that once the interim implant denture has been fabricated withthe proper occlusal determinants, aesthetics and hygiene access, thesefeatures can be accurately recorded, verified and duplicated in thefinal implant prosthesis.

Before the seventh appointment, the patient's interim denture issectioned completely in half (preferably using a fine diamond disc).Both halves of the interim denture remain stable because they aresecured via precision attachments to the implant abutments. The lab isnow instructed to fabricate a precision attachment framework. Thisframework is made in two pieces that are later resin-bonded or screwedtogether. (See Section VII.) Again, the tongue and cheek matrices areused to help provide the framework with adequate clearance for porcelainapplication. In fact, the porcelain application waits until after thesplit frame index has been taken and verified and usually involvestelescoped crowns or sections of crowns that are lingually set-screwedinto place.

At the seventh appointment, the split frame index is created. The firststep is for the framework to be tried in, in two pieces, and then tohave the male patrices resin-bonded into the framework while they arerigidly attached to the implant abutment matrix. Both sections of theframework are then removed. The right half of the interim denture isinserted and attached securely to the abutments. The left half of theprecision attachment framework is also secured into place. An index ofduralay is then taken on the left side while the patient is fullyintercuspated into the right side of the interim denture. The left splitframe index is now complete and it is checked and verified for accuracyby inserting thin film articulating paper between the opposing naturalteeth and the interim denture.

The right half of the interim denture is then removed leaving thecentric relation occlusion position held by the left split frame index.The right half of the precision attachment framework is then secured toplace in the mouth. The entire precision attachment framework should nowbe resin-bonded or screwed back into one piece. The patient is asked toclose down into the left split frame index which is mounted on the topof the left half of the precision attachment framework. A duralay recordis simultaneously taken on the patient's right side. The right splitframe index is now complete and is checked for accuracy. The entireframework and the implant abutments can now be removed from thepatient's mouth and the abutments are then screwed back down to place onthe master model. The precision attachment framework is then reseated onthe model where the accuracy of the right and left indexes are verified.The patient is given their old relined denture and healing collars untilthe porcelain crowns have been fabricated.

The split frame technique in essence allows the information contained inthe occlusal records to be accurately transferred from the temporaryprosthesis (interim denture) to the permanent prosthesis and thenverified without arbitrarily setting the vertical dimension, anteriorguidance or the centric relation occlusion of the patient. Thistechnique also allows for a slower, more gradual progressive boneloading of the bone-implant interface. This results in more healing timefor the bone (in which the implant is embedded) and allows the bone tomature.

The split frame technique utilizes the framework of final prosthesis inconjunction with the interim denture to record and transfer occlusaldeterminants. One-half of the final framework is placed intra-orallywith the adjacent half of the Interim denture securely in place to “holdthe bite”. A bite record is taken overtop of the final framework toduplicate the position of the interim denture. The interim denture isthen removed and the other half of the final precision attachmentframework is placed intraorally. A second bite record is taken overtopof this half of the framework and it now duplicates the first half. Ineffect, the interim denture has been used to “hold the bite” whileaccurate records can be developed on the final framework. When therecords are acceptable, the two halves of the final frame can be resinbonded together. The split frame technique and internal denture areespecially suited to use with UAS and MUAS components of the presentinvention, because they do not require central access bores (whichprevent true axial loading of the attachments and in fact preclude theiruse).

Context Part 3: Occlusal Considerations and Completing the Case.

The clinician now has a very accurate mounting for final porcelainapplication but because both the framework and the patrix portion of theattachment have been resin-bonded into place, direct porcelainapplication is not an option as the heat of the porcelain oven woulddestroy the resin bonds. Therefore, there are only two practicalalternatives. First is to veneer the framework with a resin materialsuch as Isocit. The advantages of the Isocit are that (a) if it is everdamaged it is easily repaired, (b) it is lighter than porcelain, (c) itis more flexible than porcelain and therefore when the framework bendsthis material it is less likely to break off (a common problem withporcelain), (d) it need not be baked on in an oven, thereby eliminatingpotential temperature distortions, and (e) the Isocit is a good “shockabsorber” during the first 1-1½ years of to bone maturation. The secondalternative is to fabricate telescopic crowns or sections of crowns withlingual set screws that can be fabricated separately frog the mainframework. This second option also has many advantages including thefact that porcelain is more aesthetic and more durable than Isocit.Secondly, if a porcelain crown is chipped, that crown or section can beremoved and repaired without having to refire the entire bridge. This isan excellent example of the ideas and principles behind prospectiveplanning.

Once the choice has been made as to which type of material will beapplied to the framework, the condylar paths of the articulator can bearbitrarily set to 20° horizontal and 15° vertical. This ensuresposterior disclusion and allows the anterior guidance to be accuratelydeveloped in the porcelain. As Dawson states “posterior occlusions thatrelate to a correct anterior guidance will automatically disclude inexcursions if condylar paths are steeper than those on the articulator.”P. E. Dawson, Evaluations, Diagnosis and Treatment of Occlusal Problems274 ch. 16 (C.V. Mosby Co. 2d ed. 1989).

Lower posterior teeth are completed and inserted at appointment eight,then the ninth appointment is scheduled for the following purposes:First, an anterior porcelain try-in of the precision attachmentframework; and second, recordings for a functionally generated path(FGP) which accurately records the precise border pathways that thelower posterior teeth follow as dictated by condylar guidance andanterior guidance. This anterior porcelain try-in proceeds with theprecision attachment framework firmly in place. Centric and eccentricmovements are checked carefully and then one final record is required atthe correct vertical dimension, but before this record is taken adequateposterior clearance must be confirmed (2 to 2.5 mm) between theframework and the opposing dentition in all excursions to allow foradequate final coping thickness and porcelain coverage

This centric record is an excellent method of verifying the accuracy ofthe articulated models. Once again, this is something that isconventionally not done routinely by clinicians because the anteriortry-in step is frequently skipped altogether and therefore the centricrecord cannot be taken at the correct vertical dimension.

Assuming that the record is accurate, the FGP record can now be taken.In many instances of full upper arch rehabilitation with implants,facial ridge resorption creates implant and subsequently toothangulations that result in rather flat anterior guidance patterns. Thisfeature makes it difficult to develop posterior disclusion, at themoment of lateral anterior guidance, without accurately recording theborder movements of the lower posterior teeth. Immediate disclusion ofthe posterior teeth at the moment of lateral anterior guidance isextremely important, for recently it has been linked to a significantdecrease in elevator muscle activity. This decrease in activity meansthat there is less force being placed on the anterior component of theocclusion and therefore less stress on the implant-bone interface.

To ensure that the upper posterior teeth disclude, the inclines of bothbuccal and lingual cusps are relieved so that only the centric stops ofthe fossae and lingual cusp tips make contact with the functional core.At this point, a matrix is made of the completed maxillary posteriorwax-ups. The wax patterns are then cut back to provide for porcelainapplication. It must be remembered that these wax patterns formindividual copings on the precision attachment framework of the presentinvention and are screw retained by lingual set screws. The wax-ups arecast and then refitted to the main framework. The matrix serves as anindex for porcelain buccal tip location. Once the buccal cusp tips arelocated, the rest of the contours are readily achieved.

Balancing incline interferences are carefully checked andeliminated—this is easily done later on in the mouth. Once all theadjustments have been made, the tenth appointment is made for deliveryof the final prosthesis. At this appointment the patient is reinstructedin oral hygiene, and a continued soft diet is emphasized for at leastthree months. The patient is seen periodically after this to assessimplant mobility and soft tissue response, because these cannot beoveremphasized as to the importance of gradual progressive implant—boneloading.

As an alternative to assembling the final prosthesis with universalabutment systems according to the present invention, other abutmentssuch as Modified UAS or MUAS with resilient cores can be placed. Thisallows for even more control over the progressive bone loading duringthe first year to year and a half when the bone is undergoing itscritical remodelling and maturation phase. Without the UAS or MUAS,these types of prosthetic reconstructions are not possible.

Context Part 4: Summary

With all the intricacies of implant prosthetic design, cliniciansfrequently lose sight of the “overall picture.” The focus must beconstantly redirected not only to deal with the effects of progressivebone loading at the implant—bone interface but also the effects thatprosthetic designs can have on the entire masticatory system. Allowancesmust be made in the prosthetic protocol to take into account the effectsthat these full arch appliances can have on the TM joints andmusculature. More time must be devoted to correcting any discrepanciesin the temporary appliance before irreversible changes are carried overinto the final prosthesis.

A recent study by Hongchen, Filin and Ning has clearly pointed out “thatthe position of the condyles in the glenoid fossa may change in theedentulous patient” as the vertical dimension of occlusion is lost. L.Hongchen, Z. Filin and L. Ning, Edentulous Position of theTemporomandibular Joint, 67 J. Prosthetic Dentistry 401-04 (No. 3, March1992). This “edentulous position of the TMJ” can be potentiallypathologic. It is therefore crucial as Hongchen, at al. point out to“correctly determine the vertical dimension of occlusion and intercuspalposition, not only for the function and aesthetic value of a denture,but also for the proper position of the condyle within the glenoid fossato prevent TMJ disorders.” Id.

Once this position is established it must be maintained accurately andmust be readily verifiable. Therefore, the idea of placing the patientin an “occlusally correct” interim prosthesis has merit.

For the edentulous patient, the interim prosthesis plays a veryimportant role; it is the cornerstone to a successful full archrehabilitation. Unless a stable interim denture is provided “you arelost at sea” and will end up approximating and arbitrarily settingcentric relation occlusion and anterior guidance. In order to create astable interim denture UAS or MUAS of the present invention must beutilized and more time must be taken before an accurate assessment ofthe health of the TMJ and musculature can be made. This allows for aslower, more progressive bone loading and more time for the bone tomature.

In order accurately to take records, transfer them from the mouth to thearticulator, and then back to the mouth in the form of a finalprosthesis, the temporaries must be stable. This is why the use of theinterim denture is so very crucial. Furthermore, without the interimdenture the split frame technique serves no purpose. The advantage inthe edentulous situation of using both the interim denture and the finalframework as part of the split frame technique is that it helps theclinician maintain solid reproducible centric stops.

If the condyles have been seated superiorally in bone to bone contactwith the Glenoid fossa and the jaw is cradled and held in this position,removing one-half of the interim denture will not create any tendencyfor the condyles to rotate, translate or for the jaw to overdose. Thesplit frame index can therefore be considered a viable alternativemethod for accurately registering, transferring and verifying thepatient's occlusal scheme.

Section II: Surgical Corrections of Ridge Doformities In Associationwith Implant Placement: Bony and Soft Tissue Augmentation

Part 1: Introduction

Dental implants are fast becoming an acceptable mode of toothreplacement; however, many of the edentulous spaces where implants areeither placed or planned have an associated ridge deformity. Thisproblem has been extensively detailed in the literature. Ibboth, Kovachand Mann state that: “Ideally a cross-sectional dimension of soft tissueto bone similar to the one found in a natural tooth should be seen . . .but as well as plate collapse occurring after loss, the authors haveobserved ridge effects that were related to traumatic tooth loss,surgical extraction, apical surgery and scarring from various surgicalprocedures.” Ibbott, Kovach and Carlson-Mann, Surgical Correction forEsthetic Problems Associated with Dental Implants, 58 C.D.A.J. 561-62(No. 7, July 1992).

Unless these soft tissue or bony defects are corrected the final implantprosthesis will be over- or undercontoured, and aesthetically as well asfunctionally it will lack a normal anatomical appearance. This cangreatly affect the patient's ability to cleanse the prosthesis as wellan pronounce certain words. It is therefore critical that associatedridge defects be surgically corrected in order to create full anatomicalcontour so that if tapered gingivectomy procedures according to thepresent invention are required, they can be performed, or if ridgelapping is required, it can be done without creating an excessivelyovercontoured prosthesis.

Ridge lapping is a very common way of dealing with aesthetic problems,as will be detailed below. The tapered gingivectomy procedure is a newmethod according to the present invention of creating anatomicalcontours but it too sometimes requires prior surgical correction ofdefects.

Part 2: Correcting Soft Tissue Defects

A transepithelial collar of minimal height, shallow sulcular depth and acircumscribed border of bound down keratinized tissue are all essentialingredients in allowing for conventional plaque control measures.

If there is a lack of attached gingival tissue or flattened papillaethen it is the surgeon's job to recreate normal gingival contours and anappropriate amount of attached mucosa. Gingival onlay grafting can beused as can subepithelial connective tissue grafts with rotated flaps.If the subepithelial graft is used it can be performed prior touncovery, but the tissue be must be overbulked and then laterrecontoured. This eliminates the possibility of inadequate bulking atStaga II uncovery but does entail an extra surgical procedure.Therefore, procedures such as autogenous gingival onlay grafting areusually evaluated at the time a tapered transmucosal gingivectomy or astandard non-flap uncovery and healing collars are planned. Whether ornot the tapered gingivectomy is to be performed, a sufficient healingperiod must first be observed if this enhancement surgery is required.For adequate soft tissue healing, a 2-month period should elapse beforeanything further is done.

Tissue guided regeneration using a reasorbable lamellar strip ofallografted bone can also be used to correct lack of attached gingivaltissue. However, this sort of surgery can only be done if bonyaugmentation is required. Assuming it is, then the lamellar strip actsas the barrier to prevent soft tissue invagination and in situationswhere the tissue has been “plugged up” by adding of extra bone or wherethere is a need for attached gingiva, the tissue can be resutured overthe strip so that primary closure is not achieved. As long as the areais not too long (4-5 mm) and the patient keeps the area meticulouslyclean, the soft tissue will, over a period of a few weeks, granulate in,creating a new area of attached tissue.

Part 3: Correcting Sony Defects.

Proper anatomical soft tissue contours are dependent on normalunderlying osseous topography. Frequently, endosseous implants must beplaced into bony sites where there is ridge deformity. This resorptionof the residual ridge occurs mainly from a buccal or labial directionresulting in ridge deformities that make it difficult to restore normalanatomical contours and shapes. In fact, the greatest reduction of theresidual ridge occurs in the early post extraction healing period from 6months to 2 years. Studies have further shown that the maxillaryalveolar process diminishes by 23% in the first 6 months and anadditional 11% in 5 years. In the mandible residual, ridge resorptioncreates a more lingually located ridge crest.

Tissue guided regeneration procedures such as onlay grafting and osseousrefilling are among the approaches most commonly employed to correctthese bony defects. As was mentioned above, one of the considerationswith these surgical corrective procedures is how they affect both thesequence and timing of prosthetic treatment. Some procedures such asautogenous bone fill or onlay grafting can be performed simultaneouslywith implant placement but only as long as there is sufficient boneinitially to stabilize the implant fixtures. Even sinus lift and boneaugmentation procedures (referred to as sub antral augmentations) can bedone at the time of implant replacement as long as there is adequatebone below the sinus to stabilize the implants.

A variety of materials can be used to rebuild a lost cortical plate,inadequate bone in the sinus area or a deformed socket. Theosteoinductive materials most effectively used are:

(a) Autogenous Transplants—These can be harvested from any number ofplaces, including the shavings from the spade drill, or from themedullary bone of the maxillary tuberosity which is rich in marrowcontaining precursor cells. If a large onlay graft is required thebuccal plate of the 3rd molar crypt or the chin button serve as goodsources.

(b) Demineralized Freeze Dried Bone.—This bone is commercially availablethrough bone banks. Sone people prefer not to use it because of thepotential viral transmission concern and decreased inductive capacityrelated to sterilization.

(c) Resorbable Hydroxyapatite—This can be synthetic in which case it(HA) lacks osteogenic activity and is more accurately classified as anosteoconductive material. The HA can also be derived from a naturallyoccurring bovine source. This material has had all of its proteinremoved and is therefore considered biocompatible.

Many clinicians use a combination of the autogenous bone (because of itsosteoinductive potential) and an allograft material such as theresorbable HA for its osteoconductive potential.

The future use of bone fill materials is likely to involve furtherresearch into “bovine osteogenic protein” which induces new boneformation in extraction sites in close approximation to the titaniumimplants within a very short period of time (3-4 weeks). For thepresent, 6 months should be observed before any progressive bone loadingoccurs around the implant bone interface.

Part 4: Conclusion.

These procedures for both soft tissue and bony defects, which can forthe most part be performed in conjunction with implant installation,function to help reestablish normal anatomical contours. Without thesesurgical procedures, ridge lapping in removable prosthetic situations orperforming tapered gingivectomy procedures according to the presentinvention for a fixed prothesis would not always be successful becauseas in standard crown and bridge procedure, the ability to produce fullanatomical contour and the correct emergence profiles is critical to asound aesthetic and functional result. This is something that someimplant companies appear to have overlooked.

In those situations when the soft tissue has been augmented to providefor a greater degree of attached mucosa, these procedures help make theperi-implant sulcus more cleansible because firm tissue is much easierto work with than loose flabby tissue.

Bone augmentation procedures are becoming more and more common,especially with the new one-step surgical phase materials such as BioCol that do not require Guided Tissue Augmentation Membranes (GTAM).

And finally, it should be remembered that clinicians should always startwith the end in mind. This means that if osseous augmentation and/orsoft tissue enhancement is required, it is preferable to do this inconjunction with the initial implant surgery-rather than have toresurgerize the area. This not only creates further delays but requiresfull mucoperiosteal elevation which in the inventor's opinion should beavoided whenever possible.

Section III: Universal Abutment Systems According To The PresentInvention

Part 1: Introduction

Universal Abutment Systems according to the present invention comprisefour basic components as shown in FIGS. 1-11:

(1) A unique tranemucosal base 10 preferably having an externallythreaded portion 12 and an interlock 14 which fits an implant 16. Thisbase 10 can be adapted to any implant system's 16 mechanical interlock14A, 14B, making it universally compatible.

(2) A preferably internally threaded core 18 which screws down andbottoms out on the base 10. From this core 18 a castable or millablecompletely customized abutment 22 is created.

(3) A shorter than conventional fixation screw 20 (with a smallervertical cantilever).

(4) An anti-rotational mechanism 24 which prevents components base 10and core 18 from rotating relative to one another when installed.

These systems feature, among other advantages as discussed in thesummary of the invention section above, a mechanism for preventingloosening of the fixation screw 20 and a unique method of housing aprecision attachment 28 within the normal contours of the abutment 22.Conventional abutment systems do not provide these features, because,among other things, many must contend with central access bores foraccommodating the fixation screw. Systems according to the presentinvention have such universal application that not only can they be madecompatible with almost every root form and blade form implant systemavailable conventionally, but also with all overdenture and crown andbridge applications as well. Furthermore, such systems can incorporateresilient core designs as shown in FIG. 6 that include resilient orelastic material 30 in the core/base interface in order to replicatearticulation of natural teeth.

Part 2: A Review of Existing Abutment Systems. Cementable Versus ScrewRetained Prostheses: Which Is better?

The inventor believes that cementing should be used only when (a) theprosthetic system cannot compensate for discrepancies in axialinclinations between the implant and the overlying crown or (b) there isconcern over the fixation screws loosening and backing out. Neitherseems to be a defensible reason for cementing the abutment or thecrown(s), however.

On the other hand, there are many advantages to the use of screwretrievable abutments. Even with the use of pre-angled abutments or UCLAtype abutments discrepancies between implant and crown axes can exist.Dr. Chiche refers to thes problem as “eccentric screw positions,” whichare simply nothing more than poorly located screws. Because thescrew-retained abutments are such a popular addition to the armaentariumof about every prosthetic dental implant company, the solution to theproblem of eccentric screw positions, screw fracture and screw looseninghas far reaching implications.

No matter what type of implant has been placed, up until present therehave only been a handful of options for the clinicians who wish to placea screw-retained abutment and a crown or bridge to correct for eccentricscrew positions. First, one can make the abutment system screwretrievable, but cement the overlying crown with a permanent lutingagent. The inventor believes that this is an unacceptable compromise intreatment. There are others that recommend the use of provisional cementbut this also has its problems.

Second, using a noble alloy, one can cast a wax pattern to an existingstraight hex/octa lock abutment or pre-angled abutment, redirecting itspath of draw for proper screw emergence using a set screw.Unfortunately, this creates extra bulk and the original prefabricatedcomponent almost always has to be ground down or altered. This oftencompromises the fixation screw and is a time consuming process.Furthermore, this method does not address the issue of screw breakageand cannot be used to incorporate intraabutment precision attachments,which will be discussed later. Perhaps even more important is the factthat one-cannot successfully cast or solder to titanium or titaniumalloy with any reliable degree of success. A seemingly acceptablemechanical bond may be created, but never a metallurgical bond, which isthe only truly stable type of bond between different metals.Furthermore, casting to titanium or titanium alloy, with a noble metal,must be done in the 1400-1600° F. temperature range. Given the meltingpoint of titanium, and depending on the grade, the risk is obviouslythat of altering the titanium's physical properties, which can obviouslylead to metal fatigue ard failure.

Third, one can fabricate an auxiliary substructure (telescopic coping)to correct the axial alignment. C. E. Rieder, Copings on Tooth andImplant Abutments for Superstructure Prostheses, 10 Int'l J. ofPeriodontics and Restorative Dentistry 437-51 (No. 6, 1990).

Fourth, one can use a plastic waxable sheath or a direct gold coping.However, it has been correctly emphasized that for severe angulationproblems telescopic copings are also required.

The first and second options are self-explanatory. The third optionmeans placing a telescopic coping and redirecting the path of emergenceof the fixation screw with a secondary set screw. This set screw can beused to anchor the overlying crown to the coping and the position of thescrews can be selected so that they do not interfere with properocclusal morphology or aesthetics. For the third option, this also meansextra steps, time, money, materials and, therefore, extra bulk.

For the fourth option, the Impac line of Vidents plastic waxable sheathsis a good example since it is said to be compatible with almost everymajor implant system. However, the Impac line seems to create its ownspecial sorts of intricacies and, in the inventor's opinion, so can thedirect coping and sheath combinations offered by Interpose ISS,Calcitek, Nobelpharma, 3I, Steri-Oss, Dentsply, AttachmentsInternational and other suppliers of conventional systems.

Use of an I.T.I. Bonefit Implant also allows for angulationcompensation, but what is unique about the I.T.I. System is that thiscompensation of eccentric screw position is made in the root part designof the implant. It achieves this with a 15° angled implant neck. (Adescription of the I.T.I. System can be found in the JPD January 1992issue.) As the authors of this article point out: “If anqulationproblems are extreme . . . telescopic constructions or primary goldcoping can be made.” G. M. Ten-Bruggenkate, P. Sutter, H. S. Oosterbeekand A. Schroeder, Indications for angled Implants, 67 J. ProstheticDentistry 85-93 (No. 1, 1992). Therefore, if implant angulations aresevere one is no further ahead with this implant system than any otherbecause the auxiliary substructure is still required, and the problemsof access bore location and screw loosening yet remain to be solved.

Contrast and comparison of the majority of conventional screw-retainedimplant systems to universal abutment systems of the present inventioncan begin simply by eliminating those systems where the sheaths are heldto a metal tranemucosal base by a fixation screw, but with no hex oroctagon mechanical interlock. These systems do not adequately accountfor rotational stability. The abutment sleeve can in fact rotate as itis being tightened down to say nothing of the potential hazard of screwloosening.

Other suppliers of conventional systems provide a more stable directconnection between the implant and the plastic sheath in the form of amachined interlock made of either plastic or metal. These systems,however, like the ones offered by ISS, 3I, Vident and Nobelpharma,cannot prevent screw loosening. In fact, none of these systems appearable effectively to prevent the fixation screws from loosening andbacking out. In the February 1993 issue of JPD, an article by Jaggers,Simons and Badr reported that “the main disadvantage of the UCLAAbutment is the potential for loosening of the retaining screw. This isrelated to frictional wear and micromovement between the titanium screwsand the internal threads of the implant body. Frequent recall visits maybe needed to tighten the screw.” A. Jaggers, A. M. Simons and S. E.Badr, Abutment Selection for Anterior Single Tooth Replacement: AClinical Report, 69 J. Prosthetic Dentistry 133-35 (No. 2, Febuary1993).

The UCLA system is the same system that Implant Support Systems states“has been called the most significant product to improve aestheticssince the introduction of the Branemark System”. Implant Support SystemsProduct Catalog (1993). In truth, screw loosening is perhaps one of thesingle biggest problems plaguing the implant industry as a whole. In the1993 Implant Support Systems Catalogue, ISS described “the problem ofchronically loose fastening screws,” which ISS blames on the“micromovemnt of the implant components and the supported prosthesiswhich can cause improperly tightened fastening screws to back out.Besides the aggravation, patient inconvenience, and loss of chair time,loose parts can also result in failure or component fractures.” Id.

The problem of screws loosening and backing out is truly a universalproblem. Companies try to solve this problem by endorsing the use of atorque wrench. Unfortunately, this does not solve the problem of theinadequately designed direct connection abutment. At a meeting of theInternational Congress of Oral Implantologists (March 1993), it waspostulated that screw loosening occurs when complete seating of theabutment in the implant is not achieved, and that it has a great deal todo with less than adequate tolerances between these parts. It is thisinventor's belief, however, that no matter how exacting the tolerancesof these parts are, a retaining screw cannot be expected securely tohold the abutment directly to the implant, for when the screw shoulderson the sleeve and attaches directly to the implant, the forces ofocclusion are directed around the neck of the screw. In a two piecesystem like the ones offered by Impact, Steri OSS, 3I and Nobelpharmathis is simply too much strain and leads to loosening and/or breakage.

Calcitak, like ISS and others, also endorses the use of thread sealantto help prevent the eventual unscrewing of abutment, attachments andscrews. Unfortunately, like the torque wrench, the occlusal loadingforces far exceed the adhesion of the sealant. This sealant is, however,excellent for preventing a bacterial buildup and the subsequent odorthat can develop around the implant ebutmts Another of the big concernsover lose parts is that they are no longer passive fitting and thereforecan frequently break under occlusal load or cause damage to theimplant-bone interface.

Apart from screw loosening and screw fracture, the retaining screws ofsome systems (particularly the IMZ, the UCLA and the direct gold copingsystem of Calcitek) which anchor the sheath to the implant, protrudeabove the implant and can sometimes interfere with the axial wallpreparation of the custom angled wax pattern.

The direct gold coping system of Calcitek is sufficiently large that italso frequently interferes with the placement of set screws andattachments. If one were to incorporate a solid core onto which a waxpattern could be cast (UAS) or an abutment milled (MUAS), and there wereno plastic sheath or bulky gold coping underneath (with an access boreproblem), it would be a much simpler and easier task to create acustomized abutment.

Another problem with the UCLA Abutment is that (and again from the ISSCatalogue) “there has been a high incidence of failure of the two piecedesigns when investment finds its way into the junction between themetal and plastic cylinder. This causes a hairline defect in the finalcasting that subsequently fractures under load.” ISS's solution to thisproblem is to use a machined, one piece UCLA abutment and a screw, ontowhich a gold alloy is cast. The problem with this solution is that it isbulky and can make restoring teeth with a lack of interocclusal distancevery difficult—not to mention extra steps and extra components, whichonce again raises the issue of time and money. Furthermore, asubstantial opening must be created to allow for the fixation screw'sretrieval. This weakens the abutment and creates a huge access channelin the crown. This large access bore hole also creates limitations as towhere additional set screws and attachments can be placed, for obviouslythey cannot be placed so that they block the access hole. The proponentsof the UCLA abutment deal with the large access opening by sailing itwith gutta percha and resin which, in the inventors opinion, is hardly apermanent solution. It must be understood that the problem of thecentral fixation screws and access bore are common to virtually all ifnot all retrievable abutment system, not just the UCLA system.

Sometimes a coping is used over the castable sheath to carry the tube ofthe screw, redirect the screw emergence, and reduce the size of theaccess opening. In the Journal of Prosthetic Dentistry April 1992 issue,Dr. Lewis and others point out that “slight angulation problems may besolved with the UCLA abutment” but that “bucally inclined implants wouldnormally result in screw access openings on the facial surface of therestoration requiring extensive steps of fabricating custom telescopiccopings.” Lewis, Llamas and Avera, The UCLA Abutment: A Four YearReview, 67 J. Prosthetic Dentistry 509-15 (No. 4, April 1992).Unfortunately, there is often not enough interocclusal space to do this.

To solve this problem many technicians attempt to use the metalframework of the crown to redirect the path of the set screw, but it isnot thick enough to accommodate a 3 or 4 mm screw. Thus, a threaded holemust also be tapped into the wall of the abutment. Unfortunately, notmany people can cast in an appropriately hard enough metal (e.g.,non-precious metal) or place a fine enough thread to prevent threadstripping or screw loosening without creating galvanic reactions orbiocompatibility problems. Companies such as Calcitek try to solve theproblem of screw loosening as mentioned earlier by recommending use of athread sealant. As it stands, altering the coping or the abutment sheathto accommodate screw fixture is not only unreliable, but is also timeconsuming and involves many extra steps.

With the direct connection that the UCLA abutment and other plasticwaxable or machined sheaths offer, there is the added problem ofverifying the fit of the casting at the level of the osseous crest.Lewis et al propose that all direct abutment restorations on multipleimplants must therefore be made as individual units and then soldered toone another, and that indexes are required to verify the fit of thesecastings. Id. All this is done to ensure a passive fitting frameworkwhich in fact does not remain passive once the retaining screws aretightened or come loose.

Universal abutment systems according to the present invention, however,eliminate these steps because the accuracy of the framework can beexplored visually due to the design of the threaded base. Another reasonthese steps are not necessary is due to the fact this resin bondingtechnology involving precision attachments according to the presentinvention solves the problem of passive fit.

Lewis et al also point out that UCLA castings with round bases can beused for multiple implant restorations. This round base has no hexconnection because, as Lewis states, “to engage the hexes on a multipleimplant could make seating the restoration extremely difficult.” Id.Lewis states that “the connection to multiple implants will prevent anypossible rotation,” but in fact, if a precision attachment appliance isused the abutments must be individually anti-rotational to prevent theattachments from lining up incorrectly. In order to bypass this problemof multiple hex-hex or hex-octagon positions and yet maintain rotationalstability, the universal abutment systems according to the presentinvention employ a unique hex, octa or other desired shape lug/recessand thread combination that is disclosed in further detail below.

Because no conventional abutment systems have this unique hex-threadcombination, they thus make it more difficult to incorporate precisionattachments and align then accurately. Even if all of the abutments andattachments can be aligned accurately, the location of the centralaccess bores prevents the attachments from being placed near the longaxis of the implants. Thus use of these types of abutments for this sortof removable appliance is simply not a realistic option.

Apart from the direct abutments such as the UCLA system or the directgold coping, almost all suppliers produce a screw-retrievableprefabricated straight or angled abutment. These are very popularcomponents, but there are many situations in implant dentistry wherethese systems do not permit the precise clinical requirements of thespecific case. This may be due to improper angulation of the implantfixture and associated aesthetic problems, or it may be due to reducedinterocclusal space or lack of a finished shoulder ledge. Similarly, thefixation screw may pose a risk of breathing or loosening. In otherwords, such conventional prefabricated straight or angled abutments arealso limited in this application.

One of the major concerns with several of these systems such as Calcitekand Dentsply is that there is no shoulder preparation allowance on theabutment sleeve, which makes it difficult to create a finely finishedmargin. The conventional pre-angled abutment or PAA's come in a varietyof angles, depending on the supplier. From a manufacturing point ofview, however, producing multiple variations of PAA's is expensive andreally not necessary since there are many instances when a customizedangle and height are required. For example, 3I produces a PAA with asecondary set screw already machined into the abutment but it has apre-set vertical and is useless if the abutment must be ground down anit frequently is.

The multiple rotational position may allow for some part of the abutmentto be parallel, but in most instances the abutment still needsalteration and this is often done very inaccurately with a resultantreduction in retention. A perfect example would be when the cliniciantries to parallel six implant abutments for a full arch fixed crown andbridge case and several of the implant fixtures are poorly angled.Unless the clinician is prepared to go to the extra trouble of makingtelescoping copings, the pre-angled abutments must be dramaticallyaltered—to such an extent that the abutments lose their retentivenessand the crowns frequently end up being cemented, or an overdenture isplaced.

Plastic waxable sheaths and direct gold copings are not the answereither, because of the problems posed by the access hole of theretaining screw and its potential for loosening. As discussed below, theuse of a coping may solve the problem of “draw,” but it is frequently animperfect solution for it involves many extra steps, more money andbesides, the old abutments under the coping still utilize an elongatedfixation screw which can be subject to undue stress.

The prosthetic system offered by Calcitek, the Integral Omniloc System,is a perfect example of why telescopic copings are required inconventional systems. Even with its pre-angled 15° and 25° abutments,auxiliary substructures are endorsed when there are discrepanciesbetween implant inclination and the facial crown contour. Calcitek, infact, subscribes to the idea that simplicity is a key requirement forits abutment system, “to minimize the number of components used.” Theinventor believes that Calcitek's endorsement of telescopic coping iscontrary to the basic premise of simplicity. Calcitek is not alonehowever, for none of the other conventional implant systems provide abetter solution. The use of an auxiliary substructure to parallelabutments also creates aesthetic compromises, for as the margin of thetelescopic coping is brought more occlusally to parallel the coping, ametal collar which cannot be masked appears. This problem does not occurwith the UAS.

Many angled abutment systems suppliers claim that their products can bealtered by grinding down the metal and then re-waxing the custom shapenecessary, but this is both a time consuming procedure and one whichdoes not readily correct for eccentric screw position. straight hex andocta lock abutments of Steri OSS, Nobelpharma, Calcitek, Dentsply, 3Iand others are examples. Furthermore, achieving a metallurgical bondbetween the titanium alloy and other metal is questionable due to theincorporation of an oxidation layer. As a result a purely mechanicalbond is created which in the inventor's opinion is not adequate. Theadded bulk of the cast to abutment also inevitably interferes with theplacement of set screws and precludes the use of intraabutmentattachments.

In the case of Dentsply's Titanium Abutment (TLT), which is a one piecescrew system, the abutment can theoretically be altered simply bygrinding down the metal, then casting it. The problem with this systemis threefold. First, because it is a one piece unit, it is screwed intoplace bypassing the hex or octagon interlock between the abutment andthe implant making it virtually impossible to accurately duplicate itsoriginal orientation in the mouth. Second, a crown cannot be screwretained to the TLT if an eccentric screw position exists without eitheraltering and “casting to” the TLT which can be a suspect solution, orfabricating a telescopic coping. If these options are not employed thecrown is usually cemented. Third, the TLT cannot prevent screwloosening.

It is also important to remember that altering the path of draw of, saya conventional hex lock abutment, plus additional lateral stresses onits elongated fixation screw, can lead to screw breakage. Rather thancomplicating matters by waxing to an existing prefabricated abutment,the entire abutment system can be simplified by using a UAS. Similarproblems exist for the direct gold copings; however, they have theadditional problems that stem from access bore and screw loosening.Because this system, like the plastic waxable sheaths, has a directconnection to the implant, it is prone to screw loosening, unlike theUAS.

Many clinicians endorse the use of Plastic Castable Abutments (PCA).They too, however, have a limited application and are mostly used whenthe clinician decides to cement a single crown. Unfortunately, there area number of problems with doing this. First, the prefabricatedtransmucosal collars are a standardized width and shape which makes itcumbersome adjusting the plastic and wax portions to accommodate theoften thin friable anterior maxillary tissue. Cementable fixtures suchas the PCA are very technique sensitive, and as Chiche has stated“Unpredictability of the agents used in luting may result in eitherdifficult retrieval or premature loosening,” [McGlumphy and Papazoglou,The Combination Implant Crown; A Cement- and Screw-Retained Restoration,13 Compendium Continuing Educ. Dent. 34-42 (No. 1)] not to mentionincomplete seating. If the PCA, for example, is not fully seated theimplant abutment assembly is not stable. Clinically, if this happens itcan lead to a non-passive fit and or;cause periodontal problems. The PCAalso requires pre-angling and alteration which usually must be done inthe mouth—this is time consuming, cumbersome and less accurate than withother systems such as the universal abutment systems according to thepresent invention. Implant Support Systems (ISS) also offers a castableplastic cement on crown (COC) which is an abutment designed to bethreaded rather than cemented into he implant. However, there is a worldof difference between a cast thread and a machined thread. With a castthread, for instance, there is always the risk of damaging the implantthread.

For those clinicians who are placing implant assembly systems, thesecond worst feeling next to a loosening implant is that of a looseningabutment—one that has loosened because the fixation screw holding it inplace has broken or come loose. As described above, the use of fixationscrews in screw retained prostheses has also caused concern due toproblems with aesthetics, path of emergence and alteration of abutments.

It is also painfully obvious that the control access bore of mostretrievable systems prevents precision attachment housings from beingplaced within the contour of the abutment and thus axially loading theimplant. The added bulk created by casting or soldering the attachmentinto place not only grossly overcontours the abutment but also affectsthe attachment's physical properties. Ideally the attachment should beresin bonded within the contour of an abutment that has no centralaccess bore. This is impossible to do with conventional existingabutment designs but not with universal abutment systems according tothe present invention.

More often than not, when screws break, they break off at the threadwhich leaves them submerged in the implant. This makes them verydifficult to remove without damaging the implant. The inventor has seenmany interesting techniques for retrieving broken screws, but all ittakes is to damage a single thread of just one implant and potentiallyan entire case can be put in jeopardy.

It can be argued that the only reason these screws break is because ofpoor treatment, planning and excessive occlusal overloading of theimplant assembly. However the inventor has seen numerous cases of screwbreakage—everything from the screw-retained single tooth, to a screwretained dolder bar supported by six implants. Even though there aretimes when screw fractures can be caused by occlusal discrepancies and“sloppy tolerances” these are not the primary reason for breakage.Rather, fixation screws fracture as a direct consequence of inadequateabutment design, specifically the manner in which the abutments areconnected to the fixation screws and the tremendous strain that isexerted on them.

The fulcrum or point of “0 Force” for a fixation screw is usually at thelevel of the implant screw threads and that portion of the fixationscrew extending occlusally into the abutment sleeve acts as a verticalcantilever. The longer the screws, the greater the risk that occlusalforces will lead to screw breakage. In fact, the bending moment whichthe screw undergoes leading up to breakage is a function of: length oflever arm (cantilever)×force (occlusal load). Therefore, in an idealworld, the shorter the fixation screw, the less bending moment and lesschance of breakage. In other words it is advantageous to have a shorterscrew bearing the bending moment.

Universal abutment systems of the present invention address all of theabove mentioned problems without the need for an auxiliary substructure,and can also prevent loosening of the fixation screw.

A relevant conventional system for comparison is the Ha-Ti system whichis disclosed, among other places, in the Mathys Product Catalog[Articles in the Mathys Product Catalog and Scientific Research Papers,including Dr. G. Graber, ZWR, 100. Jahr g. 1992, Nr. 2 70-76; Dr.Ledermann, Neue Chiruraische, Konstruktive und Zahntechnische Aspekte inder Enlossalen Implantologie, Quintessenz Heft Janu. 1, 1992 43, 7-22(1992)]. According to this system abutment design, the abutment requiresno central access bore. However, that abutment or “soldering base”appears to have a very limited application. First, it is positioned soits inferior border is level with the gingival crest and so it is notemployed to develop a transmucosal gingival taper like the UAS or MUASof the present invention. Second, it has no means of preventing itselffrom unscrewing from the soldering base ring—in other words it has noantirotational mechanism and therefore cannot be used to reproduce anexact rotational position like the UAS or MUAS of the present invention.Third, no mention is made of how slide attachments could be housed inthe soldering base. There is also no mention of how the component can becustomized and reangled in situations where the implants areecentrically positioned. Another limitation is that the si precisionattachments are soldered to the “soldering base” and not anchored intocavities by resin or a casting technique as in the UAS. Fourth, theHa-Ti system does not incorporate any form of intra abutment resinbonding like the present invention in order to resolve the problem ofpassive fitting prostheses. In the internal portion of the solderingbase there is no lug or projection and thus there is no way to preventthe fixation screw from loosening. In fact, because the threads of thesoldering base and soldering base ring are not opposite to one another,the Ha-Ti design may not be stable for any purposes. Fifth, the Ha-Tisoldering base ring also demonstrates no ability to help establishpreferred non-circular customized diverging flare of the transmucosaltaper. And because this system has no capacity to create this sort oftaper, it does not benefit from the modified impression copings andcustom healing collars of the present invention. Sixth, the Ha-Tisoldering base, unlike the UAS System, cannot be modified to create aCAD/CAM generated completely customized abutment complete withanti-rotational mechanism. Seventh, unlike the UAS, whose threaded basecan be made compatible with internal and external mechanical interlocksof the various implant systems, the Ha-Ti system cannot, because it isspecific for the Ha-Ti implant and its hex interlock has a greaterdiameter than its threaded portion. Accordingly, placing a recessed hexon the soldering base would eliminate the threads. This in other wordswould radically alter the design concept of the Ha-Ti system. The Ha-Tisoldering ring also engages a ring at the same time it engages the hexof the implant and is therefore specific to the Ha-Ti Implant. Eighth,the Ha-Ti soldering ring is used as a solid soldering base whereas theUAS core 18 can be modified with slots, grooves and channels that openinternally to expose the notch on the base 10 and form a customizedsliding lock 37. Ninth, the Ha-Ti system cannot incorporate a resilientcore component 44 whereas the UAS and IUAS of the present invention can.Other differences will be apparent.

Part 3: Universal Abutment Systems.

Many features of conventional screw-retained abutment systems reflectgood design practice, especially the protruding or recessed hexagonal oroctagonal mechanical interlocks of certain specific abutments which areadapted to engage certain specific implants, and the use of a fixationscrew. However, concern arises over the design of the coronal portion ofthe abutment and the way it is anchored to the transmucosal base ordirectly to the implant. It is these aspects of the prosthetic systemand the central access bore which need to be dramatically altered, andthis is what the UAS and MUAS of the present invention accomplish.

Some systems use a two piece abutment system that anchors directly tothe implant fixture by a long fixation screw but as has been seen thesesystems experience problems with screw loosening, eccentry screwposition and screw wreckage. The three piece assemblies which consist ofa transmucosal portion, an angled post and a fixation screw exhibit someadvantages (in the inventor's opinion) over the UCLA type abutments;however they too still share conventional problems.

The universal abutment systems according to the present invention, asshown perhaps most clearly in FIGS. 2-5, feature a base 10 with amechanical interlock 14 that is compatible with any implant system. Thiscreates a totally universal component and interface to the abutmentsystem of the present invention. The coronal threaded portion of thebase 10 has a left handed thread, which engages in a counter clockwisedirection (opposite to the fixation screw which penetrates the center ofthe threaded base) and it preferably employs a worm screw thread design.The threaded portion of the base 10 receives the internal threads of theabutment core 18, which is preferably a thimble shaped component thatscrews down very precisely onto the base 10 and in fact bottoms out onthe base. The threaded portion of the base 10 and the core 18 can bemanufactured in varying heights to to accommodate the variable height ofthe transmucosal tissue and often severe inclinations of some implants.

Through the center of the base 10 a fixation screw 20 is used as it wasintended—to anchor the base 10 to the implant fixture 16 via theirmechanical interlocks 14. A standard fixation screw would emerge throughthe top of the base's threaded collar. It would need to be cut off inorder to remain slightly submerged below the top of the base 10.Therefore a fixation screw 20 which has been so modified according tothe present invention is used. It is shorter and has less of acantilever arm and for this reason is subject to less of a bendingmoment. As shown in FIGS. 2-5, the top of the fixation screw 20 featuresa (preferably) hex hole to provide for easy retrieval. Once the fixationscrew 20 has securely fastened the base 10 to the implant 16, a core 18according to the present invention can be screwed down onto the base 10.

The flat portion of the base 10 onto which the UAS core 18 bottoms outis preferably approximately 0.6 mm in height. This creates a very shorttransmucosal portion which is often advantageous when restoring areaswhere the tissue is thin and friable for it allows the crown margin ofthe customized abutment 22 to be placed on the UAS core 18 within 0.75 mof the implant. (The UCLA abutment allows only 1 mm). Using a UAS core,the taper for the crown 26 can be started further subgingivally. This isalso advantageous when the clinician needs a wore divergent restorationto help create the appearance of interproximal papillae.

The UAS core 18 is designed to “cap off” the fixation screw 20 andtherefore provides no external access bore. In order to access thefixation screw 20 the UAS core 18 must first be unscrewed. Because it isthe UAS core 18 to which wax is added and then cast to create acustomized abutment 22, this system is able to provide a retrievablecustomized abutment 22 with no central access bore.

The UAS core 18 may be machined out of a non-oxidizing metal such asceramicor or platinum iridium and preferably has a retentive sandblastedexterior surface which extends to the edge of the base 10. The core 18may also be designed with an annular ring for increased retention (abell- or other desired-shaped top can also be incorporated into itsdesign for this purpose as well). The head of the core 18 also featuresa slot in it to allow it to be screwed down onto the base 10.

On the internal aspect of the core 18 there is preferably a machinedprojection 32. When the core 18 has bottomed out, which preferablyhappens at precisely 1 rotational position, the projection 32 is alignedwith the head of the fixation screw 20. Furthermore, the projection 32is machined to such exacting tolerance that it almost bottoms outagainst the top of the fixation screw 20 head at the exact moment thatthe core 18 bottoms out on the base 10. There is, however, anintentional micro gap which forms between the head of the screw 20 andthe projection 32, but if the fixation screw 20 unscrews more than 15°or {fraction (1/24)}th of 1 turn it will bottom out against theprojection 32. If this happens the frictional rotation of the screw 20against the projection 32 acts to tighten the core 18 thereby preventingit from ever loosening. In other words the unique combination of thecounter rotational core threads and its internal projection 32 preventthe fixation screw 20 from unscrewing far enough to create a “looseabutment”.

An anti-loosening screw (sometimes hereinafter, “screw”)or similaranti-rotational means 24 is also preferably incorporated into the UASdesign to further guarantee that the core 18 will not become loose. Ifthe core 18 does not come loose then the fixation screw 20 cannot comeloose, as described above. The ALS mechanism comes in at least two basicdesigns. Both have the same function, although they both have differentapplications.

The first design, which is shown in FIGS. 2 and 3, is the “standard ALSmechanism” 34 which has an internally threaded sheath 36 through whichpasses a screw 38 with a non-threaded dog point that inserts into boththe wall of the core 18 and the base 10. This standard design bottomsout in the wall of the core 18, rather than against the fixation screw20, in order to avoid imposing lateral loads on fixation screw 20. Whenthe screw 38 is fully engaged (shouldered in the wall of the UAS core18) its dog point is flush with the internal wall of the base 10 andthus does not interfere with the fixation screw 20. In fact the dogpoint engages a machined notch 40 in the wall of the base 10.

The second design is a “modified ALS mechanism” 35, one version of whichis shown in FIGS. 4 and 5 and has a non-threaded internally taperedsheath 43 through which passes a modified screw 45 that inserts intoboth the wall of the core 18 and notch 40 of the base 10. The screw 45of this modified ALS mechanism 35, unlike the standard ALS mechanism 34,has a threaded dog point and a non-threaded shank. This modified designbottoms out on the internal taper of the sheath 43, once again to avoidimposing lateral loads on fixation screw 20. This design is very helpfulin situations of extreme angulation where the screw 38 and sheath 43have to be cut right back because the screw threads are internal to thecore 18.

Both of these anti-rotational mechanisms 24 (34 and 35) act to “lock”the core 18 and base 10 together not only maintaining an exactrotational position but also preventing them from unscrewing. This isachieved in the following manner; when the core 18 is fully seated, thescrew 38 or 45 passes through the core 18 and then engages a notch 40 inthe top of the base 10. When the screw 38 or 45 engages this notch 40 itcreates a “dead bolt effect”.

With both designs the bore holes (both larger diameter in the core andsmall diameter in the core and the base) may be formed when the core 18is assembled to the base 10. This way is simply more accurate thanattempting to try and line up the bore holes for the screw 38 or 45 intwo separately machined components.

The UAS core 18's rotational position can therefore be accuratelyrepeated because of the combination of the ALS and the precision milledcore 18 and base 10. This precise rotational position is critical andcan be achieved in different manners by other systems but not incombination with an anti-screw loosening capability or without a centralaccess bore as in the UAS. These are features that preclude the use ofintra abutment precision attachment prosthetics in other, conventionalsystems.

The anti-rotational mechanism 24 may also take the form of a slidinglock mechanism 37 as shown in FIGS. 7-11, in which the core 18 comprisestwo sections that fit together in a dovetail or other cooperatingfashion in such a manner as to insert a protrusion 39 on one sectioninto a corresponding slot 41 in the other section of the core 18 and thebase 10. This may be accomplished with the abutment 22 formed on thecore 18 in conventional manner.

Before the unique features of these ALS mechanisms 34 and 35 arediscussed in further detail, it should be mentioned that the custom waxpattern is added onto the UAS core 18. This is done by waxing around thesheath 36 or 43 and the screw 38 or 45. The wax pattern(s) can be shapedand angled as required. This may involve parallelling six misalignedimplants or a poorly angled single abutment. It may requireincorporating a step preparation into the wax abutment (not shown) orsetting a tube and screws or creating a box preparation to accommodate aprecision attachment component 78 or 80 (see FIGS. 28 and 29). All ofthese options are available. Before the wax pattern is finalized themargin must be created to reflect the scalloped contours of the labmodel, which assures that the margins are positioned subgingivally. Thismargin for the crown 26, that will be formed later, must extend belowthe ALS 38 for reasons that will become more evident below. At this timethe precision attachment component 78 or 80 (be it, for instance, anintra-abutment slide attachment) can also be secured into the wax at theappropriate angulation and in the appropriate position. The precisionattachment 28 can also be added to the abutment 22 after casting, if awax cavity is created for it. As will also be explained below, theattachments 28 can subsequently be resin bonded to place.

The wax pattern(s) are now ready to be cast to the UAS core 18—theimportance of the ALS sheath 36 or 43 now becomes readily apparent,since it is used to protect the ALS screw 38 or 45 threads during thecasting process when the wax abutment (not shown) and the UAS core 18are cast to become a solid one piece custom cast abutment 22.

The ALS sheath is left extending out from the side of the core 18 untilafter the abutment 22 is cast; only then can the screw 38 or 45 and thesheath 36 or 43 be cut down so that they are flush to the axial wall ofthe abutment 22. Once the exact screw length is determined a slot can becreated on the head of the screw or a pre-slotted screw 38 or 45 can beused.

After the abutment 22 has been cast (preferably investment cast usingconventional techniques based on the wax-up abutment 21), the metalframework for the crown 26 can be fabricated and once this framework hasbeen firmly anchored down on the abutment with a screw block or intraabutment precision slide attachment the ALS mechanisms 34 or 35 cannotloosen simply because it cannot back out. Frameworks can easily becreated with as little as 75-100 microns micro gap fit so with the screw38 or 45 being flush with the abutment 22, it too is within 75 to 100microns of the crown's framework. Because the dog point of the screw 38or 45 engages 0.4 m (nearly 400 microns) into notch 40, it is thereforephysically impossible for the screw 38 or 45 to back out far enough todisengage the notch 40.

If the anti-rotational mechanism 24 cannot come loose not only can theexact rotational position of the abutment 22 be maintained but also theabutment 22 cannot come loose and therefore neither can the fixationscrew 20. This simply means that the entire abutment system remainsfirmly in place.

The UAS allows the anti-rotational mechanism 24, with considerableflexibility, to be located labially on anterior teeth and mesiolabiallyor lingually on the posterior teeth. This is done by rotating thethreaded base 10 so that the notch 40 is properly positioned andprovides proper access for the dentist when tightening and loosening thescrew 38 or 45.

Both anti-rotational mechanisms 24 are also designed so that they can beinserted into the UAS or MUAS assembles before they are fully seated.This prevents mishandling of the mechanism 24 in hard to reach areas ofthe mouth. As mentioned earlier, anti-rotational mechanism 24 also aidsthe UAS and MUAS assemblies in reproducing an exact rotational position,because they will only engage the notch of the base 10 in one preciserotational position. This one position is where the outer and inner boreholes in the core 18 and base 10 align. Therefore, one can verify thatthe core 18 is completely seated when the screw 38 or 45 can be screwedall the way in flush to the axial wall of the abutment 22. This uniqueanti-rotational mechanism 24 never comes in contact with the fixationscrew 20, unlike in other systems. This provides an independent andreliable means of confirming the proper fit of the components of thepresent invention to the implant 16 (unlike the UCLA system, forinstance, which must be examined “microscopically” for suchconfirmation.

The UAS base 10 and core 18 assembly also allows for the totalretrievability of a crown and bridge prosthesis without the need of atelescopic coping or auxiliary substructure or the worry of eccentricscrew position. Just as importantly, its design strengthens the abutment22 and totally prevents any chance of the fixation screw 20 loosening orbacking out. Because the fixation screw 20 cannot loosen and is not indirect contact with the abutment 22, it cannot extricate itself either,unlike other systems.

The UAS system can be used for many other applications as well, forexample, alignment and parallelling of multiple abutments (see, e.g.,FIG. 32). This system can also, as mentioned earlier, provide forplacement of intra abutment precision slide attachments, set screws,grooves and ledges, which make the prosthesis patient removable.

Perhaps one of the most obvious choices for using the UAS system is inthe restoration of the anterior tooth. Many reasons can be given as towhy these crowns should be screw retrievable and not cementable, butperhaps the beat reason is that the screw retrievable crown will allowrepairs due to porcelain fracture or accidental breakage. It is alsoimportant to note that a screw-retrievable crown allows for proper softtissue evaluation and calculus debridement around the implant base. Upuntil now, however, one of the biggest problems with the screw retainedcrowns has been causing the screws to emerge through the cingulum areaof the anterior crowns. This has been the leading reason why so manycrowns have been cemented. This off angle fixation screw often createssome very challenging situations for both the restorative dentist andthe oral surgeon. Unless the implant can be placed at the exactangulation, the proper screw position is difficult to achieve. Withother systems, if screw retrievability is essential, then the only wayto correct for this angulation discrepancy without using a telescopiccoping is to alter and cast to an existing prefabricated abutment orplastic sleeve. In this situation, a secondary set screw is used toredirect the screw emergence. Unfortunately, even if the properangulation can be achieved using these methods, once again the use ofthese other abutments can lead to screw loosening and breakage.

The alternative solution is to use the UAS in conjunction with asecondary set screw such as a screw block which can be placed so that itexits perpendicular to the lingual framework of the crown. In fact, itcan be placed in a horizontal position if the cingulum locationinterferes with a centric stop. An added feature of this system is thatthe set screw 42 can be placed into the wax abutment 21 withoutinterfering with the fixation screw 20 and then cast to place, ratherthan tapped with a crude screw pitch into the abutment 22 after thefact. Lingual secondary set screw placement is rapidly becoming a commonfeature in other systems for it does not require a large access opening.However, with these other systems, major modifications are required.

With the UAS, no matter what the angle, the assembly allows for idealscrew position, full retrievability, a stronger abutment, no risk ofscrew loosening and a more simplified approach to treatment. There arefewer steps involved for the patient, dentist and technician when theUAS is employed.

Part 4: Resilient Core UAS

Another example of the UAS's flexibility is its ability, as shown forexample in FIG. 6, to incorporate a resilient component 30, preferablyin the core 18, which helps the implant 16 and abutment 22 replicate theperiodontal membrane of natural teeth. This is particularly importantwhen splinting ankylosed implants to mobile natural teeth because theseresilient components 30 are able to absorb and distribute occlusalstress to the bone/implant interface more evenly than metal to metalimplant components. If both the implants and the natural teeth are ableto function in the same basic manner then combining them as part of thesame prosthesis becomes more acceptable. There are other advantagesgained by splinting natural teeth to implants, including: (1) providingthe prosthesis with a sense of proprioception that hitherto only theintact periodontium of the natural dentition can provide; (2) unless theteeth and implants are splinted it becomes very difficult to equilibratethe patient's occlusion accurately as the teeth are mobile and theimplants are rigid and (3) implants when splinted to periodontallycompromised teeth provide added stability and support.

The IMZ Implant Company, perhaps among others, has developed a number ofways to splint implants and natural teeth using its Intra Mobile Element(IME). IMZ provides at least two versions of the IME: (1) its threadedIME whose external threads make direct contact with the internal threadsof the implants and with which metal tranceucosal tissue extensions mayalso be used, and (2) a newer version of the IME component referred toas “IMC” and which is disposed above a threaded metal tranamucosalelement. Both versions, however, have internal threads through whichpass the main fixation screws. These fixation screws in fact passdirectly through the overlying crowns, thus leaving external accessbores. Not only are they unsightly but if even moderate angulationdiscrepancies exist between implant and crown, a complicated T blockscrew system must be employed to correct these discrepancies. Thisobviously involves more screws and more components. Furthermore, the useof a system with a central access bore precludes the use of intraabutment and intra coronal attachment prostheses. The IME componentsalso contain a circular nonrotational upper sleeve which makes itimpossible to reproduce a rotational position exactly, such as for asingle tooth application or a precision attachment patient removablebridge. Another limitation is that conventional IME's have centralaccess bores which obviously preclude the use of intra abutmentprecision attachments. The same problems of screw loosening apply to theDME as well, and the potential for screw breakage is greater because ofthe lengthy “vertical cantilever” that the main fixation screwdemonstrates. The IE itself is very specific to the IMZ implant andtherefore cannot be readily converted to be compatible with otherimplant systems. Furthermore, the upper sleeve of the IME is anunsupported projection of plastic which takes a tremendous load and istherefore at far greater risk of breakage. Dr. Howard Kay, a notedclinician, admits that “breakage of intra-mobile elements are notuncommon.” H. B. Kay, Free Standing Versus Implant—Tooth InterconnectedRestorations: Understanding the Prosthodontic Perspective, 13 Int'l J.of Periodontics and Restorative Dentistry 46-69 (No. 1, 1993). Kay alsostates that “the broken copon ent can be readily retrieved and replaced”and that “I.M.E.'s break before undue stress is transferred to theimplant/bore interface.” Furthermore, IME's do not permit easy retrievalbecause in disassembling the prosthesis the main fixation screw has tobe removed which totally removes any rotational stability the prosthesismay have had.

Another interesting limitation of the IME is that in order to splint theimplant to the natural tooth, an extra coronal cantilevered screwattachment system must be used (which to begin with is bulky). However,there are situations where there is insufficient space between theimplant and the natural tooth to place such a screw system, thusrequiring the lab manually to “mill in” a thread into the crown in orderto accommodate yet another screw. Once the IME's have been used to helpsplint natural teeth and implants together these screw systems make itvirtually impossible to create patient removable prosthetics. Thislimitation creates problems associated with ridge lapping and is whyposteriorally some create “high water” designed prostheses forperiodontal access.

Another problem with the IMZ system is that all these screws create a“pre-stress” in the system and thus bending moments related topre-loading and tightening down the screws. This in turn causes problemswith passive fit.

The resilient core version of the UAS aims to address these problems,thus allowing more flexibility in design and performance.

When a “resilient core” 44 is incorporated into the UAS assembly, theassembly may be referred to as a “Modified UAS.” The resilient core 44is designed so that its internal threads mate with the threads of theUAS base 10. The external irregular, such as hex, shape of the resilientcore 44 then engages a hollowed out correspondingly internally shapedmetal core 18. The resilient core 44 is thus “sandwiched” between metalcomponents leaving no unsupported plastic surface. The interface betweenthe metal core 18 and the resilient core 44 depends on frictionalretention but can be glued if desired with no effect on retrievability.

Once the metal core 18 has been placed on top of the resilient core 44the assembly can then be customized in the same manner as the UAS waswith one important difference. Before the metal core 18 and the waxabutment are invested and cast the resilient core 44 insert is removedso that it does not“melt”. It can simply and easily be replaced afterthe casting procedure because alignment is guaranteed by the hexinterconnections and the anti-rotational mechanism 24.

It is evident that when a resilient core 44 is utilized there are smallbut significant changes that must be incorporated into the design of theUAS base 10 and core 18. For example, the notch 40 in the base 10 mustbe deepened to accommodate for the resiliency of the resilient core 44.This helps prevent the ALS mechanisms 34 or 35 from bottoming out metalto metal which be antithetical to the purpose of the resilient core 44.

The Resilient Core UAS may, similar in some ways to the UAS, contain aprojection 32 so that when the system is occlusally loaded this plasticprojection 32 can deform into the hex hole of the fixation screw 20. Itstill, however, provides a surface against which the fixation screw 20will, if it unscrews, bottom out against.

Once the metal core 18 has been customized and cast it becomes evidentthat there are once again no access bores and no need for screwattachment systems to join or splint the implants and natural teethtogether. This neans at least two things: (1) precision slideattachments can be incorporated to the customized Resilient Core UASabutment and (2) because of the precision slide attachments theprostheses can be made patient removable which allows the prostheses tobe ridgelapped and overcontoured if necessary for aesthetics.

Another small Resilient Core UAS modification to the UAS design is thatthe resilient core 44 may be threaded down onto a threaded base 10 whichis designed with an extended 2 or 3 mm or more transnucosal collar. Thisdesign alteration allows the plastic insert to remain hygienicallyaccessible in the peri-implant sulcus as shown in FIG. 6. Even though itis now visible, the beauty of the patient removable prosthetic design isthat the resilient core 44 can be covered over and hidden by ridgelapping porcelain and metal without the associated risk of periimplantitis.

It is important to remember that the resilient core 44 does notinterfere with the anti-loosening capability of this system for thefollowing reasons, among others: (1) the modified UAS core 18 still hasan internally recessed bore hole, against which the anti-lockingmechanism 24 solidly rests so that it is stable and when the overlyingcrown is in place it cannot back out; and (2) as was mentioned earlierthe projection 32 will still stop the fixation screw from backing out.

Part 5: Variable Height Universal Abutment System.

The variable height UAS assembly is yet another example of theflexibility of the present invention. In situations where there isexcessive soft tissue depth overlying the exposed implant there is aneed to create a heightened or elongated version of the UAS base 10, thefixation screw 20 and the UAS core 18. If a resilient core 44 in to beused then an elongated resilient core 44 must also be fabricated.

The base 10 can be readily manufactured in different heights. Thevariable height base 10 would then have a varying number of externalthreads. The UAS core 18 would be machined accordingly.

As already mentioned, it is not uncommon to find areas in the mouth withvarying thickness of tissue coverage, or where the implants are allplaced at different heights. The variable height UAS was developed sothat if there was 6, 7 or 8 millimeters of soft tissue coverage thisassembly could provide a longer and more gradual taper. The variableheight UAS was also designed to allow the notch of the variable heightbase 10 to be located at or near the gingival crest. This allows thecrown margin to be extended below the anti-rotational mechanism 24 andsecure the UAS.

The variable height UAS should be thought of as a tissue extension whichsimply adds more flexibility to the UAS.

Part 6: Conclusion.

Perhaps the biggest concern that clinicians face today regarding implantdentistry is its seemingly endless assortment of techniques, terminologyand product. Each company has what it considers to be the mostcomprehensive range of prosthetic options. However, it is in the bestinterest of all these companies to simplify everything as much aspossible. Unfortunately, the product catalogues seem to be gettingbigger and more complex rather than smaller and simpler.

The UAS, on the other hand, is the simplest approach to retrievableimplant prosthetics—it is also the most practical, especially whencompared to some of the alternatives, such as the telescopic coping, theplastic sheath and/or the direct gold coping or the “altered abutment”.

The UAS is a simple four piece system that can provide both the dentistand the lab technician with the greatest range of prosthetic optionsavailable. In fact this abutment system can be easily modified toreplace the full range of all screw retrievable prosthetic abutments,including those that incorporate a Resilient component. This creates farless confusion for the dentist and the lab technician because therewould be far fewer parts and more standardized procedures for allsystems. This also means that there would be less inventory to contendwith. From the manufacturer's point of view a superior job could be donewith fewer machined parts giving rise to increased profitability.

There are many other advantages of the UAS. In the full arch situation,substructures are usually cast or soldered to one another creating acontinuous metal framework that is either cemented or screwed down,allowing no individual access to the implant abutments themselves. Thisis not the case with the UAS, because their frameworks are made to beprecision attachment patient removable which allows access around theindividual abutments. This in turn makes oral hygiene easier.Cleansability is an important factor.

Because the UAS has no telescopic components, assembling anddisassembling the device is also less time consuming, far less expensiveand something the general restorative dentist should feel comfortabledoing. As far as the dental lab and the dental implant companies areconcerned, the UAS creates an unparalleled standardization of techniqueand inventory.

In fact, the UAS simplifies all crown and bridge procedures, whereasconventional telescopic systems complicate treatment considerably. As wewill see later on, the UAS can be used in all types of implantreconstructions, not just crown and bridge applications. There is alsoless stress on the oral surgeon who is placing the implant fixtures whenhe or she has the flexibility to place the implants in the mostappropriate surgical site, knowing that the axial inclination does nothave to be such a critical decision when the restorative dentist isusing a UAS.

Furthermore, the use of an auxiliary substructure to parallel abutmentscreates aesthetic compromises, for as the margin of the telescopiccoping is brought more occlusally to parallel the coping, a metal collarwhich cannot be masked, appears. This problem does not occur with theUAS.

For the restorative dentist, a modified analog impression (see SectionIV) of the implant fixtures at the time of uncovery is all that isrequired. With the UAS, abutment selection is not required. The UAS canbe made to function in any number of ways. It could, in fact, befabricated without a set screw or a precision slide attachment whichwould allow the dentist to cement the overlying crown for whateverreason.

It is this author's opinion, however, that most clinicians favor thefully retrievable assembly to the cementable system. Not only does theUAS significantly reduce the risk of screw breakage and screw loosening,but perhaps equally as important, it allows the clinician to make everyprosthetic situation fully retrievable.

Up until now, various levels of retrievability have existed forcase-specific reasons. However, it is the inventor's opinion that thisexists only because of the design limitations of the specific prostheticabutment systems. Those situations where the abutments are screwed inand the prosthetics are cemented are simply due to poor screw emergencepatterns and compromising esthetics. Full retrievability only makessense, for how would the clinician deal with a cemented prosthesis ifthere was a porcelain fracture? Certainly the clinician would not risktapping or cutting the crown off and damaging the underlying implantassembly.

Up until now, companies and clinicians alike have been trying to dealwith prosthetics using prefabricated abutment systems. Why? Crowns,inlays and veneers are not made in this manner—they are all custom madeto fit each individual case. The abutment systems should be converted toinclude this same custom capability. After all, as clinicians we can allappreciate the difference between a prefabricated parapost and acustomized gold cast post and core.

Many companies believe that they can create a custom abutment by castingto and altering a prefabricated titanium abutment. However, as wementioned earlier this not only creates extra bulk but incorporates anoxidation layer. When precision attachments are to be incorporated intothese abutment designs their central access bores also prevent them.

Waxing over top of a ground down abutment is a waste of both time andmoney, especially when the same result can be achieved by using lessmaterial and fewer steps. It is also important to remember that alteringthe path of draw of devices such as an HLA (Dentsply Hex Lock Abutment),places additional lateral stresses on its elongated fixation screw,which can lead to screw breakage. So, rather than complicating mattersby waxing to an existing prefabricated abutment, the entire abutmentsystem can be simplified by using a UAS.

As mentioned earlier, the same basic problems exist for the direct goldcopings. However, they have the additional problems of dealing withscrew loosening. Because this system, like the plastic waxable sheaths,has a direct connection to the implant, they are prone to screwloosening. The UAS is not. As far as the fixation screws are concerned,the longer the screw the greater the potential bending moment that thescrew is subjected to. The shorter fixation screw of the UAS allows theassembly more readily to absorb the occlusal loading forces and resistbreakage.

Secondary set screws are frequently employed in premanufactured angledabutments. The set screw threads come pre-tapped into the occlusalportion of the abutment. However, they usually come in only one heightand are limited to a pre-set angulation (i.e., 3I's angled abutments).And so if the implant is severely angled or there is a lack ofinterocclusal space, then these abutments are of absolutely no use atall. With the UAS, the set screw can be placed in any position and atany angle.

Another important feature of the UAS is that the crown and the abutmentcan be removed without disturbing the rotational position of theprosthesis. The base 10 and the anti-rotational mechanism 24 alwaysmaintain their one exact rotational position for the UAS. This meansthat there is far less trouble in re-establishing the originalorientation. This can save hours of lab and chairside time.

The UAS is the first truly universal abutment system because not onlycan this one system be used to design all types of implant prosthesesfrom the single tooth and overdentures right on up to the removablecrown and bridge appliances, but the UAS can also be made to fit everymajor implant system on the market today including both root form andblade form endosteal implants. In this respect it is the base 10component that can be manufactured so that its machined interlock 14“mates” exactly with the implant 16, whether it is an external orinternal interlock, octagon, hex or tapered core.

Depending on the system, the mechanical interlock 14 between the base 10and the implant 16 may change but the external threads of the base 10and the core 18 always remain as a constant no matter what implant isused. Because of this common feature this system can “blend” differentimplants into the same prosthesis. Furthermore, it also allows aresilient core 44 component to be compatible with any system on themarket because it fits on top of the base 10. This creates a brand newmarket for a lot of companies.

The UMA (Universal Modification Abutment) from Attachments Internationalclaims to have the same type of universality but, upon closerexamination, the UMA still has the problems of an exposed central accessbore hole. Furthermore, the UMA is screwed into the implant and there isnothing stopping it from unscrewing, for there is no mechanicalinterlock between it and the implant. Therefore, the UMA may becompatible with other implant systems however, it has a very limitedapplication because it shares the same conventional problems that facethe rest of the abutments.

Finally, the flexibility of this UAS will be further demonstrated inSection V which describes a unique now process that allows customizedUAS's to be constructed in the dental lab from a pre-machined block oftitanium using CAD/CAM technology according to the present invention.These now custom milled abutments are called “Milled or MachinedUniversal Abutment systems” (“MUAS”).

Section IV: The Tapered Transmucosal Gingivectomy, the ModifiedImpression Coping, the Locking Healing Collar and the Universal AbutmentSystems: A Combined Technique to Eliminate the Need for Ridge LapProsthetics in Implant Dentistry

Part 1: Introduction.

The use of a Tapered Transmucosal Gingivectomy procedure in conjunctionwith a Locking Healing Collar, both according to the present invention,and UAS/MUAS Assemblies can eliminate the need to ridge lap implantsupported crowns that are either cemented or screwed into place. Thiscombined technique also ensures proper cervical margin placement, softtissue emergence profile and hygiene access. This procedure can beachieved without flapping or elevating the periosteum, which allows thesoft tissue and the bond to heal faster. This Locking Healing Collar isdesigned to hold the gingival tissues in any number of fully customizedanatomically contoured shapes—the outline of which is determined by theTapered Transmucosal Gingivectomy procedure according to the presentinvention. And finally, because the peri implant sulcus has been taperedand contoured the final prothesis can be secured into place withoutridge lapping the tissue which effectively eliminates the risk of periimplantitis.

In 1990 there were between 550-650,000 implants placed in the UnitedStates alone; as more and more implants are placed, the need to createaesthetic and hygienic restoration grows. J. E. Bentley, Surgical DentalImplants, J.A.D.A. (Monograph, August 1993). Up until now, the optionsfor creating aesthetic restoration have been very limited. One of thebiggest concerns is the constricted emergence profile of the implantsupported crown, which frequently creates a need aesthetically to ridgelap the tissue which in turn creates a hygienic access problem. This isespecially true in those situations where the clinician chooses to makethe restoration screw retrievable.

The conventional UCLA abutments a other direct connection abutmentspresently on the market aim to create a more divergent restoration bystarting the crown contours well below the gingival crest. The hope wasthat this would allow for a more natural soft tissue emergence profile.The proponents of the UCLA system claim that this would eliminate theneed to ridge lap the tissue as much. Unfortunately this system andothers like it cannot totally eliminate ridge lapping, for this requiresmodification to both the abutment system and the surrounding softtissues. (Many articles about the UCLA abutment still pictureridge-lapped crowns.) J. Beumer III and S. G. Lewis, The BranemarkImplant System: Clinical and Laboratory Procedures ch. 5 (FIGS. 149A andB, 150, 151), pp. 228-29 (Ishiyaku Euro-America 1989).

Because a universal solution to the constricted neck of the crown hasnot been found, restorations are either designed in a high water fashionor ridge lapped. For aesthetic reasons, ridge lapping the tissue hasgained in popularity in recent years, but once again the concern thatridge lapping creates is that it mothers the peri implant sulcus andmakes it extremely difficult to cleanse. Ridge lapping does create moreideal contours and cervical margin placement, as well as the“appearance” of good soft tissue emergence, but, it does so at theexpense of the gingival tissue and can frequently lead to periimplantitis.

The solution to this problem has two parts: (1) use of an abutmentsystem that starts diverging down by the implant and that can accuratelyreplicate the more anatomically contoured shapes of the tissue; and (2)(in order to create these more anatomic contours) the tissue itself alsomust be altered. Precursors to this technique have shown promisingresults but have required periosteal elevation, placement of astandardized conventional healing collar, and subsequent to thatplacement, modification of the transmucosal tissues. H. Israelson, J.Plemons, Dental Implants: Regenerative Techniques and PeriodontalPlastic Surgery to Restore Maxillary Anterior Esthetics, 8 Int'l. J. ofMaxillofacial Implants, 555-61 (No. 5 1993).

By using the Tapered Gingivectomy Technique, the Modified ImpressionCoping, the Locking Healing Collar and a UAS or MUAS Abutment accordingto the present invention, exacting control over the shape of the periimplant sulcus and the crown emergence contour can be achieved.

Part 2: The Tapered Transmucosal Gingivectomy: Description of theTechnique.

With this technique, it is important to ensure that all necessary stepshave been taken to create a “fully contoured” edentulous space over topof the implant. If the ridge is not fully contoured the gingivectomyprocedure should not be performed. Thus, it behooves the surgeon and therestorative dentist carefully to pre-plan the treatment and determinebeforehand whether or not the implant placement will require boneaugmentation and guided tissue regeneration.

Assuming that the ridge has been properly prepared, then 3-4 monthsafter the initial implant placement an impression of the implanted archis taken and poured in stone to create stone model #2. Using accuratefull contoured diagnostic wax ups 46, the missing teeth to be replacedare added to the stone model #2 and an outline of their scallopedasymmetrical gingival contours are then traced in pencil onto the stonemodel 48 as shown in FIG. 23. The wax patterns can then be carefullyremoved and put aside, and the pencil lines can be extendedinterproximally, without the lines touching so as to provide room forthe papillae. A red line is then carefully extended 1-2 mm inside theblack pencil lines, but reproducing the same curved asymmetrical shape.This is a crucial step for two reasons: (1) it helps establish a snugfit between the gingival tissues and the final prothesis, and (2) it isthe development of these asymmetrical scalloped contours that give riseto the unique shapes of the Tapered Gingivectomies and is what sets themapart from the cuff-shapes that the conventional symmetrical healingcollars create.

A template is then pulled down over this Model #2 and the red lines areagain carefully traced onto the clear template, which is referred to asthe “gingivectomy template” 50 as shown in FIG. 24. Next, that portionof the gingivectomy template 50inside the red line is cut out andcarefully trimmed back until the operator can barely see the outsideedge of the red line which leaves a small amount of the templateoverhanging the red lines on the model. Before the template 50 iscompletely cut back flush with the model #2 48, the depth of soft tissuecovering the implant 16 must be recorded on the model 48. This can bedone at either of two times: (1) by the oral surgeon at the time ofimplant placement, at which stage a fairly accurate measurement of softtissue depth can be provided; or (2) after the implant surgery when thegum has healed, the patient's tissue can be probed down to the depth ofthe cover screw. Either way is acceptable—an x-ray can also be of greathelp.

The depth measurement is transferred to the model #2 by creating a depthcut in the center of the template hole. That portion of the overhanginggingivectomy template 50 can now be removed in the following manner.Specially tapered lab burs or conventional burs are used to hollow outthe stone model area within the template hole down to the depth cut, andwith light lateral pressure on the bur the template is quickly expandeduntil it is flush with the red lines on the model #2. As a result, theconically shaped burs not only create a natural asymmetrical taper onthe model 48 but also on the walls of the template 50. This taper actsas the surgical guide for the Tapered Gingivectomy procedure. Thetemplate 50 is now complete and can be cold sterilized in theappropriate manner before it is taken to the mouth.

Part 3: Locating the Implants.

Using the original surgical template from model #1 the clinician shouldbe able to locate the center of the implants and mark the overlying softtissue with an indelible marker. If the surgical template is notaccurate due to anatomical or surgical corrections that were made at thetime of the implant surgery, then a periodontal probe, an Nd: YAG laser,the Siemens Periotest or other means can be used to locate the implantsand they can be marked accordingly.

Once all the implants have been “marked” the Gingivectomy Template 50can be inserted into the patient's mouth. The first thing the clinicianchocks for is to see whether or not all the implant markers lie withinthe holes of the template. To start, the clinician should only work onthose that line up. It is important to make sure that all of theimplants have a solid band of attached gingiva up to and beyond theperiphery of the template holes. If there is inadequate attachedgingiva—stop. Autogenous gingival grafts must be placed before one canproceed any further. Assuming that this has now been done, or that therewas initially adequate attached gingivae, the next step is to take asmall tissue punch and remove a tissue plug, while staying within theconfines of the template holes. This should expose the implant coverscrew. The cover screw can then be removed; however, if there is newbone growth over the top of the implant, then it mist be carefullyremoved with a low speed bur. After the screw has been removed any andall tissue tags around the implant are also removed.

This is usually th extent of uncovery with a tissue punch, the resultbeing an exposed implant with a straight or slightly flared butsymmetrical gingival cuff. Up until now the only other alternative hasbeen to raise a flap and lift the periosteum. However, this is a veryrisky procedure in the inventor's opinion because no matter howconservative the flap design the operator runs the risk of disturbingthe periosteum and damaging the blood flow to the implant-boneinterface. This can have damaging effects if the implant is bone loadedincorrectly or prematurely. The Healing Collars that are placed when thetissue is flapped are all symmetrical. Some of the very latest designssuch as the 3I healing collars have a flared shape to them but theircross sectional shape is still round. R. J. Lazzara, Managing The SoftTissue Margin: The Key To Implant Aesthetics, 5 Practical Periodonticsand Aesthetic Dentistry 1-7 (No. 5, 1993). This does not accuratelyreflect the shape of a natural looking crown and its supporting softtissue. Furthermore, the healing collars and transfer analogs are thesame size and shape which means that the final prosthesis will notexpand the tissue at all. This will create a lack of tension around thegingival tissue and allow for potential food and bacterial entrapment.

Assuming that the tissue plug has been removed and the gingivectomytemplate 50 is in place one cannot help but notice the large irregularamount of tissue that appears between the tissue punch hole and the holein the template. In some cases there is only a small amount of excesstissue but in other areas there are significant amounts. It is at thisstage that the clinician can begin to appreciate the difference betweencreating a standard symmetrical gingival cuff and a customized gingivalcuff shape that is different for every tooth/implant according to thepresent invention.

It is this excess tissue that must be removed down to the constrictedneck of the implant to create the asymmetrical naturally contouredTapered Transmucosal Gingivectomy. This can be don carefully with ascalpel while pressing down on the template 50 to keep the tissue firmlyin position or with the aid of special gingivectomy burs. There is alsonew clinical support mounting for the use of the Co₂ and Nd: YAG lasers.If these lasers could be used without risk of damaging the implant itmay prove to be an effective method of performing the TaperedGingivectomy.

After the tapered Gingivectomy has been performed the template 50 can beremoved. Once the hemorrhage has been controlled appropriately sizedModified Impression Copings 52 as shown in FIG. 25 can be placed intothe implants 16 and screwed down firmly to seat. The unique design ofthese copings 52 allows the operator to get an accurate impression ofthe surrounding tapered transmucosal tissue 54 and at the same time geta transfer impression of the implants' position. This can all beaccomplished in one simple procedure because the flat side of thecopings 52 help create rotational accuracy and the annular rings whichextend below the gum line help create an accurate impression of thetapered tissue 54.

The impression is usually taken with a polyvinylsiloxane material 56 andwith the Modified Impression copings 52 in place as shown in FIG. 25B.The material 56 is carefully syringed around the base of the copings 52and once the material has set the clinician has an accurate impressionof both the implant 16 and the surrounding tissue 54. Even if thecopings 52 are in perfect alignment a direct analog impression techniqueis preferred so as no to disturb the impression. There is considerablepotential inaccuracy in repositioning the copings 52 back into theimpression (indirect transfer analog impression technique) and suchrepositioning should therefore be avoided if at all possible. Asdiscussed below in this Section, the direct analog impression techniqueis not always possible, especially when the implants are severely angledsuch as in the posterior less accessible areas of the mouth. Once thecopings 52 have been unscrewed and removed a set of UAS base 10's andfixation screws 20, described in Section III above, and which can laterbe retrieved and reused, are inserted into the implants 16 and Barricaidlight activated periodontal wound dressing is syringed around them. Thismaterial serves to hold the tissue 54 in place and allows initialhealing until the Customized Locking Healing Collars 58 according to thepresent invention have been fabricated. The patient's denture ortemporary is hollowed out and relined to accommodate the threaded base10's and Barricaid.

Modified Implant Analogs 53 as shown in FIG. 27 and as discussed belowcan then be attached to the Modified Impression Copings 52 in theimpression and the impression can then be poured in a dental stone. Thismodel is referred to as the Master Model #3.

A Flexible Modified Impression Coping 51 according to the presentinvention may be required when creating a tapered gingivectomy around anoff angle implant. See FIGS. 26A and B. As far as misaligned implantsare concerned: If when the Tapered Gingivectomy Template is placed, theimplant 16 appears to be slightly beyond the hole, a tissue punch cannotbe used. Instead, a scalpel or other implement must be taken and angledthrough the template hole to gain access to the implant 16. This createsa tapered transmucosal cuff with a slight undercut. This undercut,however, is removed when model #3 is lab altered. If a standardimpression coping or even one of the inventor's MIC's were used in thissituation, it would press or penetrate through the gum at some pointbeyond the tapered cuff. A normal MIC would extend straight out of theoff angled implant and not only distort the Tapered Gingivectomy butcould also create the wrong soft tissue emergence position. In off anglesituations, especially in the back of the mouth, this also makes itdifficult to get a direct transfer analog impression. This is whatfrequently gives rise to crowns with exposed transmucosal necks or oddlycontoured cervical (neck) contours.

The solution to this problem is a Flexible Modified Impression Coping 51according to the present invention (“Flexible MIC”). The base 55 of theFlexible MIC is similar mechanically and in appearance to the metal baseof the Locking Healing Collar, perhaps with a lower profile flange. Ontothis base a flexible plastic tube or coping 57 can be positioned.Normally this plastic tube would have to be screw retained to the metalbase. The plastic coping 57 may, however, feature an internal machinedmetal snap interlock which is both precision fitted and removable. Theoutside wall of this plastic coping 57 has a pleated collapsible section59 which allows the sheath to be bent.

Once the Flexible MIC 51 has been bent into position so that it exitsthrough the tapered gingivectomy hole and so that impression materialcan be syringed around its base, (see FIGS. 26A and B) it must berigidly fixed to place. This is achieved by simply providing light curedacrylic down the ‘hollow’ of the sheath (the head of the fixation screwmust first be lubricated). Once the acrylic sets up it holds theFlexible MIC 51 rigidly in position. Once impression material has beensyringed around the tapered cuff to capture its contour and the materialhas set up around it, the Flexible MIC 51 will snap off the metal basewhen the impression is removed remaining firmly anchored in theimpression.

The advantages of these Flexible MICs are at least threefold.

(1) They allow for all impression copings to be aligned parallel or nearparallel, which circumvents the problems associated with inaccuracy andimpression taking of off-angle copings.

(2) The Snap Removable Flexible MIC creates the ability to remove thisMIC sheath off of the metal base and be held accurately in theimpression.

(3) They allow the integrity of the Tapered Gingivectomy to bemaintained, transferred to Model #3 and then lab altered as usual evenif it is undercut.

Once the metal base has been unscrewed from the mouth, it can beattached to a modified impression analog 53 (“MIA”) (FIG. 27).

Once the MIA 53 is assembled to the base of the flexible MIC, a plastictube 61 is snapped onto the distal end of the MIA 53 (theend poking outof the impression). This assembly (metal base/MIA/screw/plastic tube)can now be snapped into the flexible MIC plastic coping 57 which ishoused in the impression. Exact rotational position is maintained bysimply aligning a small groove present in both the metal base and theflexible MIC plastic sheath. The assembly is left poking up at an oddangle out of the impression. Die stone can now be poured into theimpression and around the assembly. Die stone must never be poured abovethe level of the plastic sheath attached to the MIA as this channelprovides access to the screw holding the assembly together. When thereis more than one flexible MIC and MIA, assembly the stone is only pouredup to the top but not beyond the level of the lowest plastic tube. Oncethe stone is set, the impression tray can be removed and with it theflexible MIC sheath snaps off of the metal base. The Master Model #3 canbe carefully turned over and the MIA screws backed out. This will allowthe metal bases to be removed and will leave the Modified ImplantAnalogs in the Master Model #3 complete with their surrounding TaperedGingival Cuffs which can then be lab altered.

One of the most important features of the MIA system is that after thelab altering procedure is completed and healing collars have been made,it allows the UAS wax up to be held securely in position from theunderside of Master Model #3. This means that the base 10 and core 18 donot have to be anchored to the implant 16 by the fixation screw 20. Thisfurther means that once the UAS core 18 is waxed up, the core l8 and thebase 10 do not have to be unscrewed from one another. They can simply bepulled straight off the model. This preserves the anatomicallyasymmetrical taper of the wax up. This can only be done using an MIA butrequires that the MIA screw be undone before attempting to remove theUAS wax up.

As was mentioned earlier, a most important feature of the flexible MICis that it allows all of the impression covings in the mouth to bealigned. In the posterior jaw, where there is limited access, screwingstandard impression copings to place is not only difficult to do but ifthey are off angle, the risk of distortion is increased.

Whether the impression contains Flexible MIC's or MIC's, it is thenrepoured using a new set of regular implant analogs, but this time witha GI soft tissue mask around the implants. This Model is referred to asModel #4 and its significance will become apparent later.

On Master Model #3 the modified implant analogs and the taperedtransmucosal sulcus should now be evident. They may appear to besomewhat jagged in shape but they accurately represent what is in themouth. This Master Model #3 must now be “lab altered” to recreate thecustomized gingival tapers. This is why the red line was drawn insidethe fully contoured pencil lines, so it could now be enlarged. This fullanatomical taper on the Model #3 will allow the customized healingcollars to stretch the gingival tissue to full contour without damagingthe tissue and at the same time create a snug fitting gingival cuff.

To lab alter Model #3 accurately, the Gingivectomy Template 54 must beused. It is first replaced on Model #2 and the full contour black pencillines are traced onto the template 54. The template is then enlargeduntil the black traced line is removed. The template now represents“full anatomical contour” and can be positioned on Model #3 so that thecontours of this model can also be enlarged using conventional orspecial gingivectomy lab burs with rubber tips that protect the modifiedimplant analogs from damage while the contours are being enlarged. Oncethese contour changes have been made, the diagnostic wax ups 46 can bepositioned on the Master Model #3 to confirm that it accuratelyrepresents “full anatomical contour.” Master Model #3 can now bereferred to as “Lab Altered Model #3”.

Locking healing Collars 58 as shown in FIG. 1 may now be inserted intoLab Altered Model #3. Such collars 58 include a base 60, preferablyformed of a non-oxidizing metal (such as Ceramicor), which is adapted,as in the UAS base 10, to engage the top of the implants 16 in lockingfashion, and unlike the UAS base 10, to receive a plastic sleeve 62 inits upper portion. [These will be secured in place in the mouth to theimplant 16 by a fixation screw 64 (which shoulders on the inside of theplastic sleeve 62).] On model #3, wax can now be added to both the metalbase 60 and the plastic sleeve 62 of the Healing Collar 58 to create amore divergent collar and one that fills the “lab altered cuff”. Annularrings on the wall of the plastic sleeve 62 help ensure that the waxpattern is anchored solidly to the Healing Collar 58. The wax patternthat is formed on the outside of the plastic sleeve 62 is built up tothe crest of the cuff, and the sleeve 62 is left extending up beyond thewax pattern so that a prothesis can later be attached. The fixationscrew 64 which shoulders on the inside of the sleeve 62 can be removed,as the wax pattern now holds the metal base 60 and the sleeve 62together as one unit, and is now ready to be invested. The inside of thesleeve 62 can either be invested and the crew seat redefined aftercasting with a reamer, or an alternative method can be used to removethe fixation screw and insert a graphite or ceramic analog which can becast to and then sandblasted out afterwards. If the metal base 60 ismade of a non-oxidizing material such as ceramicor or platinum iridium,the wax pattern and sleeve can be cast to it in Type IV gold whichcreates a strong metallurgical bond and is biocompatible with thetitanium implant.

The newly cast Locking Healing Collars 58 can be polished and returnedto the patient's mouth whereupon the Barricaid can be removed and theLocking Healing Collars 58 secured to place. As was mentioned earlier,the unique design of these Locking Healing Collars 58 allows theslightly oversized collars to fit snugle into the mouth compressing thetissue just enough to provide a firm fit. Note that some blanching doesoccur but excessive pressure is prevented by controlling the contours inthe mouth and on lab altered model #3. If excessive pressure is appliedthis can lead to gingival clefting and recession. This is a commonproblem with many of the existing abutment systems. They force thetechnician arbitrarily to create arbitrary anatomic shapes without firsttapering the tissue slightly and second, accurately contouring andcustomizing the healing collars.

As was mentioned earlier, 3I has attempted to solve this problem byrecently developing largo tapered healing collars and implant transfercopings. The problem with 3I's approach is that the healing collars aresymmetrical and therefore do not represent anatomically correct softtissue contours. Furthermore, the healing collars and the transfercopings have already determined the full soft tissue contours for thecrown before the master model has even been created. This means that thecrown ends up being the same shape as the healing collar—a standardsymmetrical shape.

With the Locking Healing collars 58 in place the tissue has now reachedits full anatomical contour and is given several weeks to heal. TheHealing Collars 58 are then progressively loaded. In the partiallyedentulous situation or the single tooth replacement situation, thetemporaries are in fact left out of occlusion for the first few weeks.

It must also be remembered that in the completely edentulous situationthe Tapered Gingivectomies are not performed but the Locking HealingCollars 58 are still placed and the denture is simply relined with asoft liner.

If necessary a screw block can be added into the hollow open end of theLocking Healing Collar sleeves 62 s0 that temporaries can also be screwretained. Either resin temporaries with non-precious metal cores can beused to add stability and strength or normal at processed temporariescan be used to load the bony architecture progressively. As wasdiscussed earlier in Section I these temporaries can remain in place forupwards of 3-4 months.

Once this healing phase has been observed the final restorations can befabricated. However, the exception to this rule is in the fullyedentulous situation where there are no custom tapered transmucosalcuffs and the final abutments can be placed at an earlier stage toanchor the interim denture (as discussed in Section I).

Note that in all other situations where these gingivectomies have beenperformed new impressions do not need to be taken after the healingphase for two reasons (1) there is very limited tissue shrinkage withthe Tapered Transmucosal Gingivectomy technique, and (2) the lab alteredcontours are already present on Lab Altered Model #3.

However, before the final abutments and prothesis can be fabricated onefinal alteration must be made to Lab Altered Model #3, which has to dowith the appearance of the tissue in the patient's couth around theLocking Healing Collars 58. Remember that the Locking Healing Collars 58are structured 80 that their flat base portion on which the temporarysat is level with the gingival margin on the stone model. Frequently,however, the gingival tissue does shrink, ever so slightly, and becausethe base of the Locking Healing Collar 58 was initially fabricated levelwith the gingival crest this can be examined intra-orally and anyshrinkage can be compensated for on Model #3. This is simply done byshaving down the occlusal gingival height of the cuff on the model by amillimeter or more, especially at the labial or interproximal sites.When the final abutment margin is prepared it is level to Model #3 whichis now lower than the gingival margin in the mouth. In effect theclinician is “lab altering the Lab Altered Model #3” one final time.After this has been done, it can be referred to as the “Final LabAltered Model #3”. This shrinkage of tissue is but one more very goodreason why the fabrication of the final prothesis should not be rushed.With existing technology, new soft tissue impressions would be necessaryespecially when the tissue is flapped to expose the implants and allowsfor tissue shrinkage.

As an added control step, the customized abutments with their finalmargin placement can be tried in to reconfirm proper margin location. Ifnecessary the margin can easily be altered.

In order to ensure that the abutments 22 and the crowns 26 will bedivergent enough to fill the custom tapered gingival cuff 54, UAS orMUAS assemblies must be used (See Section III & V). A direct connectionabutment such as the UCLA is not recommended because: (a) of problemswith screw loosening and access base location, and (b) they are directconnection abutments and to create a tapered crown their margin starts 1mm above the neck of the implant which is difficult to check clinicallywhen the soft tissue coverage is 3-4 or more am thick. Prefabricatedabutments with so-called more anatomically correct contours such asthose that 3I endorse cannot be used because they are prefabricated andcannot reproduce the individualized custom tapers and contours of thetapered transmucosal cuff. Furthermore, these 3I abutments, likevirtually every other abutment system on the market, also have centralaccess bore and if screw loosening problems. The only logical choice isthe UAS or MUAS assemblies so that contours can be developed to matchthe gingival tissue exactly. There is also no worry of screw looseningwith these assemblies.

When the UAS/MUAS abutments are ready to be fabricated, the importanceof Soft Tissue Model #4 becomes apparent. Because of the design of theUAS core 18, once it is cast to form the customized taper it is oftenasymmetrical and therefore will not thread down to place on the stonedie of “Final Label Altered Model #3.” This is why Soft Tissue Model #4is required. On Model #4 the core attachment 22 can expand the flexibleGI Mask and allow for complete seating of the components. Furthermore,Model #4's soft tissue profile has not been altered like Model #3 and sothis allows an accurate means of checking the final crowns 26, marginplacement and emergence contours.

It should be emphasized that when the wax UAS abutment 21 is beingcontoured to the “Final Lab Altered Model #3,” once the wax up iscomplete it cannot be rotated off of the Model without breaking the waxpattern. The reason once again has to do with the customizedasymmetrical tapers that are being created on this Model. There are twosolutions to this problem: First, before the core 18 is screwed downonto the base 10 the threaded base 10 must be firmly anchored to theimplant analogue. This is achieved by tightening down the fixation screwuntil the machined interlock 14 is fully engaged. The fixation screw 20is then backed out. If the machined interlock 14 does not have a Moore'sTaper incorporated into its design, the base 10 be secured down with alittle sticky wax. Only then can the core 18 be threaded down to place.After the wax abutment 21 has been created and the anti-loosening screwis in place the entire core 18 and base 10 can be lifted straight out ofthe implant analog by holding firmly onto the ULS mechanism 34 or 35.This prevents having to rotate the wax pattern off of the stone modeland damaging the wax pattern. Second, a Modified Implant Analog(described earlier) can be placed which allows the UAS base 10 to betemporarily anchored from the underside of final lab altered mastermodel #3. Before the base 10 and core 18 can be removed, the MIA screwmust be backed out.

It is in situations such as these that conventional systems are limited,for they feature less flexibility to address off angle or customizedcontoured cases.

With the MUAS System, since there is no waxing or casting to thecomponents, this is not even an issue. After the custom tapered waxpattern has been cast (UAS) or the abutment has been custom milted froma premachined titanium blank (MUAS), the abutments 22 can be screweddown onto the threaded base 10's on Model #4 because its gingival cuffis made of an elastic deformable GI mask material.

Part 4: Fabrication of the Overlying Crown.

The UAS or MUAS base 10's can also be secured down with a fixation screw20 onto an analog and the abutment 22 can again be secured to the base10. In this fashion, the components can be handled as if they were anindividual die onto which a framework and porcelain can be built upusing the transmucosal taper of the abutment 22 as a guide for propercontour. Model #3 can also be used to create the proper emergenceprofile and occlusion for the crowns 26.

Part 5: Conclusion.

It is evident that there is a need for the Tapered TransmucosalGingivectomy procedure in the partially edentulous jaw, and it isimportant to note that by custon tapering the transmucosal cuff theclinician can enjoy the following advantages, among others:

1. Make the peri-implant sulcus more accessible for oral hygienepurposes.

2. Provide better aesthetics than ridge lapping for the crown can nowtruly emerge through the gingivae with the cervical contours of anatural tooth.

3. Eliminate the need for ridge lap prosthetics which many cliniciansbelieve is one of the leading causes of peri implantitis.

4. Provide more natural lingual contours since the relief of thepalato-gingival area is not required for hygiene access.

5. Avoid unnecessary periosteal elevation which allows the gingivaltissues to heal more rapidly.

6. Avoid placing Healing Collars then having to come back and takeseparate Transfer Analog Impressions.

7. Create interdental papillae by compressing the tissue and creatingcrown with the proper mesio-distal width.

The problem of ridge lapping was said to have been eliminated with themost recent introduction of certain “anatomically correct” abutmentsystems. However, without first altering the width, taper and contour ofthe tranemucosal cuff, ridge lapping cannot be entirely eliminated.

Another very important consideration is that of periosteal healing. Manysuppliers of conventional systems endorse the use of a full thicknessmucoperiosteal flap at the time of implant uncovery. No matter howconservative, the flap design studies have shown that elevating theperiosteum results in a risk of necrosis and slow remodeling of thecortical plate which, if incomplete at the time of second stage surgery,will load necrotic or immature bone resulting in excessive corticalcrater formation. With this in mind it becomes obvious that ifperiosteal elevation can be avoided then it should be avoided. Thesolution is to use a Custom Tapered Transmucosal Gingivectomy procedurewhich does not require a flap approach. When this procedure is combinedwith a Modified Impression Coping, a Locking Healing Collar and a UAS orMUAS, the combined technology provides for optimum aesthetics andfunction.

Finally, the flexibility of this system is perhaps best illustrated bythe incorporation of Flexible MIC's and MIA's. These components allowthe clinician to correct for off angle implants and to deal with waxingto the UAS core regardless of the peri implant transmucosal taper. Thefollowing is a summary of the steps of the tapered gingivectomyprocedure according to the present invention:

1. Using preliminary wax up teeth to set tooth position for missingteeth, create a surgical template using model #1.

2. The surgical template aids the dentist in placing the implants. Thistemplate is saved during the 4-6 month healing period.

3. Before implant uncovery, an impression of the mouth is taken. Asecond stone model is created and accurate full gingival contourdiagnostic wax ups are created on this model. Using the initial surgicaltemplate to indicate implant position, outline these accurate fullanatomical contours on stone Model #2 with a black line.

4. on Model #2 create a redline 1.0-1.5 mm inside these outlines.

5. Make a clear template on Model #2 (“Gingivectomy Template”).

6. Trace the red outline markings onto the Gingivectomy Template.

7. Remove the template from Model #2 and using a bur, slowly enlarge theholes up to the red lines, exposing the red lines on the model.

8. Before replacing template on Model #2, create depth cuts in the modelto replicate approximate depth of soft tissue coverage (measured byprobe).

9. Replace the Gingivectomy Template on Model #2.

10. Angle bur and enlarge the template until red lines on modeldisappear. This is done to a predetermined depth (depth cut). Enlargingthe model creates a flare on the Gingivectomy Template.

11. Place surgical template from model #1 in mouth and place a dot wherethe implant center should be.

12. Remove surgical template and place Gingivectomy Template in thepatient's mouth. Check to see that implant dots line up with holes.

13. With the Gingivectomy Template in the mouth, start removing gingivalmucosal tissue. Using a tissue punch, remove a plug of tissue and exposethe implant.

14. Between the border of the tissue punch hole and the GingivectomyTemplate there will still be excess tissue. Using a bur, scalpel, Nd:YAG or CO₂ laser, remove this tissue to form a taper from the annulus ofthe implant to the perimeter of the Gingivectomy Template creating ananatomically tapered gingival cuff, of specific individual dimension andcontour.

15. Place modified implant copings or Flexible MIC's onto implants andsyringe impression material into the tapered transmucosal sulcus. Aftermaterial has set, remove impression copings. This will transfer tomaster model #3: (a) the tapered cuffs; and (b) the axial and rotationalposition of the implants.

16. Insert modified implant analogs onto the modified implant copings,and cast stone model #3. Threaded base 10s are screwed into mouth and alight activated periodontal wound dressing is syringed around then tohold tissue contours and promote healing (Barricaid).

17. This stone model which contains modified implant analogs and showsthe actual tapered gingival cuffs as they appear in the mouth is mastermodel #3. A second model is created from the same impression using a newset of modified implant analogs. However, this model is created with aG.I. mask. This model #4 is used to replicate the resiliency of thetissue in the mouth and is not lab altered.

18. Lab altering requires the tapered Gingivectomy Template to beexpanded with a bur to the original black line which represents fullanatomical contour.

19. Place the Tapered Gingivectomy Template after it has been soaltered, on master model #3, and using gingival burs, carefully enlargethe taper on the model to the enlarged outline of the altered gingivaltemplate. This causes the healing collars to be formed slightly largerthan the taper in the mouth and creates firm, but not excessive,pressure against the tissue.

20. Place locking healing collars into the lab altered model #3 and:

(a) Add wax around the metal base and plastic sleeve up level to thegingival crest;

(b) Use hot wax casting techniques to create a cast locking healingcollar with a fully customized anatomically contoured taper;

(c) Create a temporary crown on the locking healing collar;

(d) Return locking healing collar to mouth and secure after removal ofwound dressing (Barricaid) and threaded bases (installed in step 16).

21. Before the final abutment is fabricated, the tissue is allowed toheal, which requires that the implant/bone interface is slowly andprogressively bon* loaded over a period of months. This is controlled bymodifying the temporary crown.

22. Once the tissue has healed, master model #3 requires one furthermodification. The occlusal-gingival height of the stone model #3 isshaved down slightly to compensate for any tissue recession and to hidethe margin of the crown. Master model #3 is now referred to as “PinalLab Altered Model #3.”

23. Using final lab altered model #3, fabricate a UAS or MUAS. If theprosthesis is not removable, then all these abutments incorporate thecustomized anatomically correct tapered gingival cuff.

24. Once the abutment has been fabricated, model #4 is used to createproper margin position and contour for the overlying prosthesis, ie.crown.

Section V: The Milled Universal Abutment System (MUAS): Breaking NewGround With CAD/CAM.

Part 1: Introduction.

“Of all the new technologies available to dentists, none is more likelyto drastically change the practice of dentistry in the 21st century thanthe Dental CAD/CAM.”

Francis Duret, May/93 CDA Journal

At one end of the dental spectrum are dental implant companies usingvery elaborate CNC drilling machines and sophisticated CAD software tocreate very precisely machined prefabricated implant components.However, their biggest limitation is that these standardizedprefabricated components are all exactly the same. These systems cannotproduce individually customized components [e.g., conventional angledtitanium abutments (“ATA's”)].

At the opposite end of this spectrum is the dental CAD/CAM technologythat digitizes information from the individual patient's mouth usingoptical scanning to create a customized restoration for the individualpatient. Its limitations are (1) its accuracy 80-100 microns and (2) thefact that the dental CAD/CAM system is used only to create crovns,inlays, onlays, area veneers and in more select instances, bridges. Theuse of material is also basically limited to ceramics. P-R Lin, B. P.Isenberg and K. F. Leinfelder, Evaluating CAD-CAM Generated CeramicVeneers, 124 J.A.D.A. 59-63 (April 1993); F. Duret, The Practical DentalCAD/CAM in 1993, 59 CDA J. 445-51 (No. 5, May, 1993); Siemens MedicalEngineering Group Dental Sector, CEREC Computer Reconstruction, CERECPamphlet.

It is evident that each technology has limitations, which is perhaps whyto date no one has applied this CAD/CAM more completely in the implantfield. Perhaps the closest that any one company has come is the Procerasystem which can, using a combination of external surface milling andinternal electro-erosion, produce titanium crown and bridge frameworks(for ceramic coating). Unfortunately, this is the extent of its implantinvolvement.

In order to apply CAD/CAM technology more completely in the implantindustry and fabricate customized implant abutments, a combination oftechnologies is required—a blend of CNC milling and customized CAD/CAMcapabilities. The result is a breakthrough technology which the presentinvention accomplishes by allowing implant abutments to have all oftheir exacting threads and interlocks pre-machined into a titanium blockusing a CNC milling machine or similar device and then having thatabutment's customized external contours milled into that titanium blockusing Dental CAD/CAM that has in the past been reserved for ceramics andcreating custom fillings. The result is a very precise fitting,completely customized abutment, for use in the Millable UniversalAbutment System, and which takes the place of the core and cast abutmentin the UAS.

Part 2: Description of the MUAS.

This unique new combination of technologies creates an unparalleledpotential for the entire implant industry because a totally customizedimplant abutment can be created not only by a wax added and castingtechnique (in the UAS) but now by mans of a CAD/CAM system (the MUAS).Both methods have the same anti-screw loosening capability as well asmany other solutions to common abutment problems.

The titanium blank 66, shown in FIGS. 12-16, which may be milled by theCAD/CAM System, is unique in that a CNC or comparable milling machinehas been used to pre-machine a core thread 70, the core projection 32and an anti-rotational mechanism 24 thread or similar anti-rotationalmeans directly into the titanium blank 66. In other words, it looksalmost identical to the UAS core 18. As disclosed further below,modifications can also be made to the titanium blank 66 in order toincorporate the design concept of the resilient core 44 into the MUAS.

It is important to remember that these premachined titanium blanks 66fit precisely to the base 10 because these components have been CNCmilled together in order to align the anti rotational mechanism 24thread hole and notch 40 correctly. Whether the base 10 has an externalor internal machined interlock 14 with the implant 16 also makes nodifference to the fit of the base 10 and the titanium blank 66. In fact,the titanium blank 66 can be looked upon as a bulky oversized core 18and the bulk of the titanium above the threaded section is for practicalpurposes a mass of metal that can be milled to any customized angle orshape using a dental CAD/CAK.

This procedure is achieved by using the Lab Altered Master Model #3, asdescribed in Section IV. The Master Model #3, before it is altered, isan exact duplicate of the tapered gingivectomies and implant position inthe mouth. The transmucosal cuff of this stone model surrounding theimplant analogues may be altered using the gingivectomy lab burs. Therubber tips of these burs prevent damage to the implant analogs, butconventional or other burs may be used as well. The cuff is to enlarged1.0-1.5 mm so that the gingival tissue fits firmly around the crown andthe abutment. The wax patterns that were a originally used to make theGingivectomy Template 50 can now be used to check and see if thetransmucosal cuffs are at full anatomical contour. The gingival crestsof these cuffs are also altered—in fact, they are ground down by about 1mm to create subgingival margin placement for the crown. This can beverified later on Model #4, as was described in Section IV.

These lab altered steps are critical to the fit and shape of both theabutment 22 and the crown 26. When the abutment 22 is secured down toplace in the mouth it will expand the surrounding gingiva just enough toprovide a firm fitting gingival cuff. If too much tissue expansion isrequired, as is the case when a Tapered Gingivectomy is not performed,this can crush the tissue and deprive it of its blood supply, which canlead to gingival resession, gingival clefting and sloughing of thetissue.

This is why the lab altered Model #3 is preferably only altered by 1-1.5mm and why a Tapered Gingivectomy is performed in the first place.

Next comes the optical impression of the lab altered Master Model #3.This optical impression generates a digitized image of the tapered cuff54 as well as the implant 16's axial and rotational positions, usingCCD-based sensor 72 or other appropriate (and conventional, if desired)imaging components as shown schematically in FIG. 17. In order totransfer the axial and rotational positions of the implants accurately,the optical impression may taken with the threaded base 10 and anelongated fixation screw 20 securely in position. The base 10 is placedin such a way that the ALS notch 40 is accessible for the dentist. Theoptical scanner senses the position and disposition of the notch 40 andfixation screw 20 (which may be in cartesian, spherical or otherreference system as desired) and the processor and storage means of theCAD/CAM device 74 processes and stores this information and aligns thetitanium blank 66 accordingly in conventional fashion for appropriateangulation of the abutment 22 with respect to the implant 16, bothrotationally and laterally. This is especially critical when more thanone abutment 22 is being constructed as in the case of a bridge.

Digital information corresponding to the optical impression is storedfor processing by the CAD program conventionally. This program isadapted in conventional fashion to recognize that the base 10 is inposition and to compensate for this in the design of the abutment 22.The CAD program may be modified to allow the operator to designon-screen (via pen-based, mouse or keyboard input/output means 76) acustom shaped abutment 22, using an image manager (as shownschematically in FIG. 16) that allows for surface reconstruction andmodelling. This CAD program may also be modified to design a recess orcavity 68 that can be milled out for a precision attachment 28 componentcorresponding to a corresponding component in the overlying crown 26.Since one cannot cast or solder to titanium, standard laboratoryprocedures are of no use, one may use resin bonding techniques accordingto the present invention for securing such attachments.

The milling or machining of the abutment is carried out in conventionalfashion by a computer aided machine tool based on data from the opticalimpression and the clinician using the image manager. The result is acompletely customized titanium implant abutment 22 which has been madeusing CAD/CAM technology in a new way. This titanium implant abutment 22features the following advantages, among others:

(1) Is biocompatible with the surrounding tissue;

(2) Has not been cast, soldered or laser welded;

(3) Because of its physical properties, is totally inert and will evenpromote a hemidesosomal attachment in the peri implant sulcus;

(4) Is stronger than any other 2 or more piece system;

(5) Is identical to the UAS system (with all attendant advantages)except that its abutment contour is computer generated and not waxadded; and

(6) Can incorporate resin bonding of precision attachments which allowsfor new and innovative prosthetic designs.

Once the MUAS has been machined (and this also applies for the UAS), itcan no longer be rotated to position on Master Model #3 due to itsintentionally customized asymmetrical taper. This is why Soft TissueModel #4 has been created in order to allow the abutment to be fullyseated and the contours and marginal placement of the overlying crownfully visually and physically checked.

The last modification that has to be made to the abutment 22 before thecrown 26 can be fabricated and adjustment is the insertion andadjustment of the screw 36 or 45 length. Because the thread of screw 38or 45 and taper is of a standard measure in every titanium blank, astandard screw 38 or 45 can simply be inserted into the completed MUASand cut back flush to the abutment wall.

With minor changes to the shape and design of the premachined titaniumblank 66 this technology can be used to produce a MUAS, a modified MUASusing a resilient core 44 (as shown in FIG. 13), MUAS abutment 22 thatwill fit a variable height threaded base 10 and anti-rotationalmechanisms 24.

As was described above, the MUAS variable height assembly portion of thebase 10 may be made in different heights so that when the core 18 andanti-rotational mechanisms 24 are positioned they are located at thegingival crest. This can be accomplished by lengthening the base 10.These alterations also require construction of a modified titanium blankand a slightly longer fixation screw.

We know that the bases 10 can be milled or otherwise formed so that thethreaded portion is adapted to different heights and widths. The blank66 and the internal dimensions of the core 18 and its threaded portionalso have to be altered accordingly. The outer diameter of the blank 66,however, does not have to be altered and neither does the milled baseseat of the blank 66. This blank 66 can be milled down in the samemanner as the regular blank 66; all that has to be done is to input theheight of the specific variable height base into the CAD program andchoose the appropriately machined blank 66. These same types of changescan also be made to accommodate a resilient core 44.

Now that it is possible to create a precise fitting totally customizedimplant abutment 22, it should be mentioned that the manufacture ofcorresponding crowns and bridgework/frameworks from titanium is possibleusing the Procera CAD/CAM unit or similar conventional devices andtechniques.

With the combination of these technologies it is now not only possibleto manufacture precise fitting customized implant abutments 22 accordingto the present invention but also the crown 26 and bridgework to fitovertop.

Section VI: Universal Abutment Resin Bonding Systems

This section addresses use of the Universal Abutment Resin Systems(“UARS”) according to the present invention in conjunction with UAS/MUASimplant abutments 22 and intra abutment precision attachments 28.

The application of resin bonding technology in non implant relatedprosthodontic dentistry today is still very limited. Only a fewcompanies such as Cendres and Metaux, Sui and a growing number of othercompanies are endorsing resin bonding, but even these applications arelimited to joining attachments into fixed and removable portions of adenture (natural teeth). This is but a small portion of the potentialnew resin bonding marketplace.

The CM Spacer technique detailed by Cendres and Metaux has manyadvantages and can be used in conjunction with many different types ofresin product but it has limited implant application.

The potential market for resin bonding implant application is huge bycomparison and the UM has a much broader application. The precisionattachments' 28 component parts can now be resin bonded into either aMUAS or a UAS abutment using a series of new spacer techniques. Itshould be made very clear that, up until now there have been no existingimplant abutment or resin systems created for intra abutment resinbonding of precision attachments in implant dentistry. The beauty ofthis technique is that crown and bridge prostheses can now be madepatient removable, passive fitting, aesthetic, stable, hygienicallyaccessible and if necessary can be ridge lapped without damaging thesurrounding tissue and contributing to peri implantitis.

The UARS techniques can in fact be employed to join precision and semiprecision attachment housings into both the abutment and the frameconstruction of the implant prosthesis because slide attachments require2 components as shown in FIGS. 27-28: (1) a matrix component 78 which isusually housed within the contours of the abutment (intra abutment) 22and (2) a patrix component 80 which is usually passively bonded to placeon the internal aspect of the overlying prosthesis framework.

For purposes of comparison, at present one other resin bonding techniqueexists for implants, which is referred to as the Kulzer Abutment LutingTechnique (“KAL”). R. C. Olarn, W. R. Lacefield, The Passive FittingImplant Prosthesis, 4 The Implant Society 8-15 (No. 2, 1993). It is,however, used with conventional abutments that feature central bores,and it is used to join conventional UCLA type abutment cylinders to themain framework of the prosthesis in a non-patient removable fashion.

The KAL technique claims to achieve a more passive fitting prosthesisbecause a plastic cylinder (spacer) creates an enlarged hole in theframe which is taken up by the resin cement while everything is seatedpassively in the mouth. This system has obvious limitations anddifferences from the UARS technique, however:

(1) The KAL technique uses only a Kulzer Resin System—the UARS techniqueis compatible with all resin bonding systems.

(2) The KAL technique joins abutments and mainframes rigidly togetherwith resin. The UARS technique allows the abutments and the mainframe tobe separable (pulled apart via precision attachments).

(3) The KAL technique does not allow for patient removableprostheses—the UARS technique does.

(4) The UARS technique is employed to bond precision attachments withinthe normal contours of UAS or MUAS implant abutments. The KAL techniquehas no such applications.

(5) The KAL technique claims a passive fit between the prosthesis andthe implant. However, once the prosthesis has been rigidly resin bondedto the abutment cylinders the fixation screws of these UCLA likeabutments must be constantly torqued down over a period of a month inorder to prevent the screws from backing out (which they can do anyway).A. Jaggers, A. M. Simons, S. E. Badr, Abutment Selection For AnteriorSingle Tooth Replacement: A Clinical Report, 69 J. Prosthetic Dentistry133-35 (No. 2, Febuary 1993). “The main disadvantage of the UCLA Systemis the potential for loosening of the retaining screw.” Furthermore,every time these fixation screws are tightened this creates pressure(preload) between the implant and the prosthesis. When this preload issuperimposed by off axis occlusal loading forces the result can be anon-passive fit. In other words the KAL technique may start out aspassive, but as soon as the resin sets and the fixation screws areretightened it has the potential to become non-passive. Of course thesame concept works in reverse as the screws loosen and begin to backout—a non-passive fitting prosthesis.

With the UARS technique, because the abutment 22 is anti-screwloosening, the fixation screw 20 can be torqued down into place,retightened ten minutes later and then capped off and prevented fromloosening by the core 18 and ALS 24. Now the abutment 22 is secure andthe precision attachment 28 assembly can be passively bonded intoposition without being affected by the fixation screw 20. Therefore theprecision attachment prosthesis starts out with a passive fit andremains passive.

As has already been pointed out, resin bonding is the only proventechnique for the direct connection of precision attachments totitanium. Thus for the MUAS system there is no other option. However forthe UAS system, the abutment can be cast to the ceramicor core in anyalloy except titanium and therefore the attachment connection can becasted, soldered or even laser welded. Unfortunately all three of theseoptions put the precision attachment under a great deal of temperaturechange which affects not only the physical properties of the attachmentbut also, with very thin female housings, creates potential for apotential strike-through of the wall by a hot melt. Furthermore, castingon can result in an incomplete metallic union between the frame and theattachment if the correct placement of the spaces and choice of theproper volume relations in the region of the attachment are notselected.

Although laser welding of attachments 28 shows great promise, resinbonding at the present time is still the preferred method. The UARStechnique allows for the attachment component to be resin bonded toplace without incorporating the problems associated with casting orsoldering such as the stresses of temperature variation. There are otheradvantages to the UARS technique as well:

(1) It is more accurate in aligning the matrix and patrix components ofthe attachment in the mouth because it creates a truly passive fitrather than rigidly attaching the components in the lab. This option isavailable for resin bonding but not for casting, soldering or laserwelding.

(2) If the matrix or patrix components must be changed, it is easier toremove the component out of resin than it is to break the casting orsolder joint or laser weld. In fact, disconnection of the resin bondedinterface may be achieved by blasting with 50μ Aluminum Oxide or similarmaterial.

(3) The bond between the resin and the metal has been proven to beincredibly strong (6-8000 psi interfacial bond strength).

(4) The UARS technique helps eliminate many unnecessary dental lab andclinical procedures such as casting, soldering and investing.

A box or cavity preparation 68 for the attachment 22 can be created inthe abutment in a number of ways, all of which are compatible with theresin bonded technique. If an MUAS or modified MUAS is being createdthen the cavity as can be milled at the same time as the abutmentcontours. If a UAS or modified UAS is being created then the box orcavity preparation 68 can be created in at least one of three ways.

(1) The cavity 68 can be milled in after the abutment 22 is cast.

(2) A cavity 68 can be created in the wax abutment 21 and then cast,utilizing an I.N.S. spacer that exactly duplicates a portion of theprecision attachment. This creates a precisely cast cavity into whichthe other interlocking half of the precision attachment component willfit.

(3) An oversized I.N.S. spacer or similar ceramic spacer can beincorporated into the wax abutment 21, which like number (2) above canbe removed after casting with a 50μ or similar particle sandblaster. Asmore and more precision attachments 28 are incorporated into implantabutments the spacer techniques will grow in popularity, and so will themarket for these ceramic spacers. For further details on this spacertechnique see Section VII Part 3.

Once the cavity 68 has been formed within the implant abutment aduplication model is usually created. When such a model is used, analogsof the patrix and matrix components are set into the model rather thanthe precision attachments themselves. These analogs can be partiallyoversized replicas of the precision attachments which help to create andmaintain extra space in the abutment and the framework, or they can beexact duplicates of the precision attachments. These analogs alsoprevent wear and tear on the attachments. See FIG. 30B. As will be seenbelow, they can also be used to help align the precision attachmentcomponents and for this reason the mechanically interlocking surfaces ofthe analogs are exact duplicates of the attachments. Only the externalsurfaces vary in size in certain situations to maintain the extra spacefor the resin bonding material.

If a duplicate model is not going to be used then the external surfacesof the matrix component 78 can be coated with a silane coupler or otherdesirable agent and set within the abutment 22's cavity 68 which isfilled with resin. The attachment component 78 is held rigidly in itsproper position with a parallelometer and the resin sets up around it.The excess resin is removed and the matrix 78 is left rigidly connectedto the abutment 22.

The patrix component 80 which is usually housed in the internal aspectof the crown 26 or prosthesis framework can also be resin bonded intoplace either in the lab or preferably in the mouth using the same spacerconcept and silane coupler application. In order for this resin to setproperly, dual cure cements are preferred and therefore a slot or holeis created in the crown framework to allow the back end of theattachment (the flag) to extend through the frame and have thesurrounding resin light activated.

The UARS technique can be used entensively in implant dentistry incombination with these new UAS and MUAS abutment systems because thephilosophy, approach and implementation of this new technology ispassive fitting precision attachment patient removable prosthetics.

Because of increasing numbers of implant supported prostheses beingfabricated, the importance of resin-metal bonding is also likely toincrease. With the resin bonding technology of the present invention,the market in not only going to increase, but also undergo a major shiftas more and more prostheses start to incorporate precision attachmentpatient removable designs.

Section VII: Prosthesis Design: Expanding The Options

Part 1: Introduction.

Up until now prosthesis design has provided the clinician only limitedoptions, with either fixed or removable appliances, i.e. Misch'sclassification. Recently an article entitled “The Use of Intra CoronalAttachment on Removable Prostheses” appeared in the InternationalJournal of Oral Implantology, which described a ball and socket O-ringattachment for an overdenture. C. E. Misch, The Use of Intra CoronalAttachments on Removable Prostheses, Int'l J. of Oral Implantology. Inthe inventor's opinion, this is precisely why a new classification needsto be created to redefine the use of precision attachments and patientremovable prostheses. The prosthetic designs according to the presentinvention not only reflect this new classification by providing intraabutment precision attachment patient removable crown and bridgeappliances, but also new prosthetic designs for overdentures as well.The crown and bridge prostheses, for example, are just as stable, if notmore stable, than the screw-retained protheses but also have the addedadvantages of being passive fitting and able to be ridge lapped due tothe fact that they are patient removable. As discussed below, many ofsuch now prosthetic designs, such as the now overdenture bars, are notpossible with existing systems. Also detailed below is a nowclassification of prosthetic implant design based on thesepossibilities.

There are approximately 20 million people living in North America whoare completely edentulous, and world wide percentages are probably evengrater. A good percentage of these people have unsatisfactory lowerdentures. A typical case would be where the upper teeth were removedalong with the lower posterior teeth at an early age, leaving only thelower anterior teeth. These lowers were subsequently removed leaving anuneven edentulous ridge. In many instances this scenario leaves verylittle bone posteriorly (following Wolff's Law) but adequate bonebetween the mental foramina to support implants.

Implants have a high degree of predictability especially in the loweranterior region, which is the location that the inventor believes isadmirably suited for this unique style of prosthesis.

Part 2: Existing Classification of Implant and Tissue supportedOverdentures.

A. Tissue supported—Implant Retained Overdentures.

This classification usually involves only 2 implants which have a capand ball like attachment screwed to the implants and which arepredominantly located in the cuspid region. These attachments, which canalso be magnetized, act to retain the denture—the majority of supportand stability, however, comes from the tissue coverage of the denturebase.

B. Tissue Bar Overdentures.

These types of dentures are both implant and tissue supported. Theyusually involve 4 implants and can be a combination of tissue bar andresilient ball and socket or O-ring attachments, which allow for addedstress breaking as the denture is displaced towards the ridge underocclusal loading forces. The Hader clips which are usually positioned onthe anterior aspect of the tissue bar also rotate around the bar if itis oriented parallel to the axis of rotation. Even with 4 implants,distal cantilevering is not recommended without the incorporation ofresilient attachments posteriorly into the tissue bar design.

These tissue bar overdentures allow for the denture to be removed by thepatient which improves oral hygiene access, but cleaning around the bardoes pose a hindrance for some patients and this can lead to plaque andcalculus accumulation.

Because these dentures can be removed, a buccal and lingual flange canbe placed for lip support, aesthetics and phonetic advantages. However,even with 4 implants these tissue bar overdentures are still not asstable as the fixed dentures, and the tissue bars still have problemswith screw loosening, impassive fitting frameworks and lack of hygienicaccess.

C. Fixed/Detachable Denture Prostheses (The Hybrid Denture).

These appliances require a minimum of 5 or 6 implants if they are to bedone as conventionally recommended, such as by Branemark. They providefor an extremely rigid prosthesis but because it is screw retained it isonly detachable by the clinician. Furthermore, the use of an excessivevertical or horizontal cantilever with this type of a prosthesis canlead to screw loosening or fracture, bar fracture, implant fractureand/or de-integration. There is also the problem associated withframework distortion and non passive fit. This point becomes glaringlyobvious upon examination of the results of Dr. Zarb and the Universityof Toronto's 1990 longitudinal implant study which were discussed in anarticle by Monteith:

One noticeable feature among the problems and complications encounteredduring the Toronto study was the large number of gold screws that werereported to have fractured. Of 274 implants that were placed to support49 protheses, 53 fractures of the gold alloy screws were noted, 14framework fractures and 9 abutment screw fractures. Similar observationemerged from a replication study conducted at the University of theWitwatersrand in which Shakelton et al. reached the conclusion that morethan 50% of prosthetic problems are related to stress factors acting onthe prostheses . . . To have screws fracturing as a normal event wouldnot be conducive to sustained levels of patient confidence.

B. D. Monteith, Minimizing Biomechanical Overload In Implant Prostheses:A Computerized Aid To Design, 69 J. of Prosthetic Dentistry (No. 5, May,1993). The ad modum Branemark fixtures are frequently cantilevereddistally to engage an opposing molar occlusion, but English is quick toreveal that an excessive distal cantilever with inadequateanterior-posterior spread is a prelude to mechanical or osseous failure,or both.

The critical A-P Spread that English speaks of is fundamental to thedesign of existing implant/implant and tissue supported dentures.Unfortunately, surgical and anatomical restrictions often prevent agreat deal of anterior-posterior separation between implant fixtureswhich decreases the A-P spread and limits the length of distalcantilever. English clearly points out that the A-P spread has a directrole on whether one is dealing with a class I or class II lever and thatthis is accentuated by the jaw relationship.

A patient who is a known clencher or bruxer imposes forces on thecantilever that are accentuated as one moves posteriorly, which variesconsiderably according to the maxilla-mandibular jaw relationship. Thesecantilever forces are extremely damaging to the implants, for as Englishagain points out “when one places occlusal load on a cantilever segmentthe two most distal implants in the fulcrum are placed in compression ina vertical download, and the implants anterior to the fulcrum are placedin tension, i.e. a vertical pull out.” C. E. English, The Critical A-PSpread, 1 The Implant Society 2-3 (No. 1 1990). Furthermore, Falk etal., have established “that fully 70% of the occlusal forces are borneby the cantilevered units and only 30% of the occlusal load is borne bythe anterior segment.” H. Falk, L. Laurell, D. Lundgren, Occlusal ForcePattern in Dentitions with Mandibular Implant-Supported Fixed CantileverProstheses Occluded with Complete Dentures, 4 Int'l J. OralMaxillofacial Implants 55-62 (No. 1, 1989). This study concluded thatthe recently reported higher number of failures for this type oftreatment was probably the result of poor distribution of occlusalforces during mastication. C. E. English, supra. “The only way tocounteract these lever forces would be to have the lower teeth extendedanterior to the most anterior implant to provide a counterbalancingforce.” But, “unfortunately the advantage is still to the distal segmentwith increased occlusal forces”. Id. In a patient with a class IIskeletal jaw relationship, this is possible because the denture teethneed to be extended anteriorly for lip support and improved aesthetics.Unfortunately for most other cases this can spell potential overload andimplant failure.

Furthermore, because the ad modum denture is fixed into place, theabutment cylinders must be left exposed for oral hygiene access. Inother words, no buccal or lingual flange can be created, which oftencreates aesthetic and phonetic problems as well as lack of lip support.

D. The Spark Erosion lmplant Supported Denture.

This type of denture was created to: (1) solve the problem of the fixeddenture that the patient could not remove; (2) provide a buccal flangefor better aesthetics, phonetics and lip support and (3) solve theproblem of passive fit. This type of denture is created to fit over aspecially constructed tissue bar (using spark erosion technology) thathas an external 2° taper to engage with a friction fit a milled bar thatis buried in the underside of the denture. The spark erosion denture isas stable as the screw retained fixed denture but has the added benefitof being partially removable by the patient. However, these sparkerosion dentures must still use a rigid cantilever design and thepatient still has to clean around a fixed tissue bar. Furthermore, theabutments that the tissue bar is anchored to still suffer the sameproblems with component fracture and screw loosening.

Part 3: The Precision Attachment Stress Broken Denture: An Alternativeto existing Fixed/Detachable Dentures and Bar Overdentures usingUAS/MUAS Assemblies.

Abstract.

Stress Broken Precision Attachment Dentures of the present invention(“SPADs”), unlike the above appliances, can be removed as one piece bythe patient exposing easy to clean individual abutments. The SPAD is asstable as the fixed screw retained implant supported denture but it doesnot have the problems of screw loosening, impassive fit, hygiene access,cantilevered forces and framework distortion due to rotationaldisplacement that these other systems have. SPADs feature many uniquefeatures, one of which is the way their hinged precision attachments areincorporated into the fixture design so that the prosthesis functions toabsorb excessive vertical- oblique- and lateral-occlusal loads.

The Precision Attachment Stress Broken Denture.

The SPAD is a combination of both implant supported and tissue bornedenture systems. It offers the same rigidity and stability that theimplant supported denture offers and is also precision attachmentpatient removable. Furthermore, it offers superior hygiene access to theperi implant sulcus, and it prevents the screw loosening that plaguesall the other implant prostheses as well as solving the problem ofpassive fit and retrograde peri implantitis by incorporating stressbroken precision attachments into the framework design.

Computer analysis has shown that the stress levels within supportingbone imposed by axial and lateral loads applied to dental implants maybe as much as 2-2½ times greater than the stress levels created simplyby axial loading. Thus it appears that dental implants are particularlysensitive to lateral loads and that lateral loading on implants as aresult of non passive fitting frameworks may cause screw loosening,component failure and bone resorption around dental implants. Thereforelateral loading should be avoided when at all possible. Unfortunatelythis is not possible with the existing technology. However, it ispossible to absorb some of these lateral forces with the SPAD.

Perhaps one of the most exciting features of the SPAD is that all ofthese problems can be corrected utilizing only four implants. This isonce again possible because of the dentures' superior stress breakingcapabilities.

The following hypothetical case illustrates one way a SPAD may beutilized according to the present invention. UAS or MUAS assemblies areplaced on the master model and, in the case of a UAS, the UAS core waxups are paralleled. Cavities are then created in the wax patterns forthree newly designed Vertex intra abutment slide attachments accordingto the present invention, which are discussed below. (Obviously, othertypes of precision attachments could be used.) These cavities may becreated using one of two INS spacer techniques. Both methods requirethat the margins of the four UAS assemblies are located at the tissuelevel on the model leaving the ALS mechanisms 34 or 35 exposed on thewalls of the abutments.

The first method allows for only one half of the Vertex attachment to beresin bonded to place, usually the patrix component. To accomplish thisan INS ceramic spacer is placed into the wax abutment but its externaland internal dimensions are exactly the same as a matrix component.After the abutment has been cast this INS matrix spacer is sandblastedout creating an exact cavity into which a patrix attachment can later beanchored. A duplicate model can then be created by inserting patrixanalogs into the matrix cavities. From this step forward both methodsare identical.

The second method allows both halves of the Vertex attachment to beresin bonded to place. To accomplish this a matrix INS ceramic spacer isalso placed into the wax abutment but its external dimensions areoversized to coppensate and make allowances for the silane coupler andresin bonding material. After this INS spacer has been sandblasted out,a similarly dimensioned matrix analog can be inserted into the cavity.This will later be replaced by an actual matrix component that will besmaller and can readily be bonded into a passive position. Similar tomethod one, a duplicate model can be created by inserting a patrixanalog, except this time the patrix analog is inserted into a matrixanalog and not a precisely cast cavity.

In both methods these patrix analogs have external oversized dimensions,but their internal mechanically interlocking surfaces are exact replicasof the actual attachments. This allows the matrix analog to fitprecisely to a patrix attachment component. Analogs are used to preventwear and tear on the components and do not have to be retrieved from theduplicate models. They are usually made of brass and are inexpensive andcan be discarded.

On the duplicate model a wax framework is then created overtop of thefour abutments and around the oversized patrix analogs. Before it iscast, cavities are also created using INS spacers in the outside distalaspects of the frame to house two more patrix analogs. These two analogsare replicas of the two UARS stress breaking attachments. The wax frameis then cast in titanium. As mentioned earlier with method two, when theINS spacers are sandblasted out, enough space is left in the frameworkfor the attachments, the silane coupler layers and the resin, and thematrix and patrix analogs can be inserted to take the place of theattachment components.

The titanium frame is created with a double die spacer technique and istied in and adjusted until it slides effortlessly to seat. At this pointone could turn the model upside down and the framework would drop off.Remember that it is the attachments that create the retention and thestability for the prosthesis rather than the framework. The framework'sfunction is simply to transmit and redistribute occlusal loads accordingto the present invention.

Passive fitting frames play a very important part in the prostheticreconstruction phase of treatment but because precision slideattachments can now be used within the framework and the abutments, theconcept of “passive fit” must evolve to include UARS technology. Ifprecision attachments are rigidly connected before the framework isseated in the patient's mouth and they are not perfectly aligned, theywill not fully seat, which in turn creates a non passive connection eventhough the framework may be fitting passively. Therefore, it isimportant to remember that when seating a precision attachment frameworkintraorally, it should slide passively all the way into place and eitherthe matrix or the patrix of each attachment should have some “play”between it and the surrounding metal so that attachment can be fixedinto a totally passive position. This space or “play” is createdcreating one of the two INS ceramic spacer techniques.

Using method one, the matrix has already been cast as negative relief bythe INS spacer so that “play” exists between the patrix and internalaspect of the framework. This extra space or play allows the vertexpatrix to be resin bonded permanently to place. This is achieved in themouth by first placing the UAS to place and inserting the vertexpatrices into the matrix cavities. After all the components have beensilane coupled, resin cement is applied to the internal aspect of theframework (one at a time) and the framework is fully seated into thepatient's mouth. The holes in the top of the framework allow for theoverflow of resin cement and in the case of the vertex attachment, alsoleave the occlusal spreader screw exposed so that retention can later beadjusted. The cement is allowed to harden around the patrix. This resinbonding technique is repeated for all the attachments. To prevent excesscement from sticking to the UAS, a separating solution such as asurgical grade lubricant is used. Using method one the precisionattachment prosthesis is now patient removable and completely passivefitting.

Using method two, both matrix and patrix components are resin bonded.First this requires that the patrix attachments are paralleled and thenpermanently resin bonded to place. This can be done in the lab byplacing the vertex patrices into the matrix analogs on the duplicatemodel. They are now paralleled and the framework can be slid downovertop of the abutments with resin on both the attachment and theframework. The holes in the top of the framework allow for the overflowof resin cement and also leave the occlusal spreader screw of the vertexattachment exposed so that its retention can be adjusted.

The framework can now be taken to the patient's mouth along with theUAS's where the matrices can then be inserted into the permanentlybonded patrices, located on the internal aspect of the titaniumframework.

The hollowed out cavity on the UAS created by the INS ceramic spacer andthen held by the oversized matrix analog can now be silane coupled. Thespace or “play” now exists between the matrix housing and the UAScavity. The resin cement is applied to each cavity separately and theframework is fully seated. Once again the separating solution comes inhandy, preventing the framework from bonding to the abutment. Once thecement has set the female housings are permanently resin bonded intotheir passive position. This method allows for more control over theattachments' final position and allows for easier retrievability of theattachments in case of breakage. However, this method involves an extrastep. This method like method one also makes for a precision attachmentpatient removable prosthesis.

Using either method, once the two halves of the precision attachmentframework have been bonded together in the mouth, the framework and theabutments can be returned to the lab where the two patrix housings ofthe UARS stressbreaking attachments can be paralleled and permanentlybonded to the back ends of the framework. The two matrix housings arethen either cast using a ceramic spacer or resin bonded into theframework and two unilateral partial denture frameworks are then createdaround them. (Once again, duplicate models can be created but thisrequires matrix and patrix analogs.) It is not until the acrylic isbuilt up on these frameworks that the two matrix housings can be rigidlyanchored. The design of the two UARS stressbreaking attachments allowsdenture teeth to be set over top of them and totally cover the matrixhousings. Because the UARS patrix components are usually inserted intothe distal side wall of the framework and porcelain covers thisframework, they are not obvious. In other words, by the time the SPAD iscomplete the UARS stressbreaking attachments cannot be seen, for theyare totally encased. The prosthesis is in effect a one piece assemblythat has two stressbreaking hinged attachments incorporated into itsdesign. There is no lingual bar connecting the two saddle areas.

It is important to note that the only position of the titanium framethat is rigidly cantilevered is the guide rail of the UARSstressbreaking patrix component, which unlike the ad modum Branemarkframeworks that are rigidly cantilevered up to 15 or 20 mm.

Section VIII discloses how the UARS stressbreaking attachment componentsare constructed to resist heavy occlusal forces. The verticaltranslation and rotational ability of these UARS stressbreakingattachments is what helps distribute the applied occlusal forces,especially the damaging lateral forces. Without the resilient UARSstrossbreaking attachments, there is no way truly to control theseocclusal forces. Dr. Y. M. Ismail, a noted specialist in the field ofimplant occlusion and biomechanics has stated that these occlusal forcesand resultant stresses can be controlled:

before the selection and placement of implants, prosthodontic diagnosisand treatment planning must be completed in order to properly evaluateand accommodate the direction, magnitude and duration of appliedocclusal forces. It is imperative that in the final prosthesis everyattempt be made to minimize lateral occlusal forces and theirtransmitted stresses to the supporting osseous structures. This can beaccomplished by reducing the buccolingual width of the occlusal table,reducing the cusp height and angle, eliminating centric and eccentricinterferences and customizing these occlusal concepts to the individualcase.

Interview with Dr. Y. M. Ismail on Implant Biomechanics, 4 DentalImplantology Update 6-8 (No. 1, January 1993). Although it is importantto “customize the occlusion,” it is the inventor's opinion that this byitself is not enough. The full arch hybrid fixed/detachable prosthesismust be modified dramatically to incorporate stressbreaking mechanismssuch as the UARS stressbreaking attachments effectively to address theoff vertical torquing and bending moments and the mesial implant stressconcentration that occur as the result of the rigid cantilevered design.

Admittedly, the A-P spread is a vertical design factor in determiningthe length of cantilever. However, it no longer has as much relevancesince all rigid cantilevers in full arch situations beyond 5 mm shouldbe replaced with stress broken attachment assemblies.

There is also one other way of dealing with occlusal loading forces,that Ismail does not mention, and that is by modifying the actualabutments. This can be done by inserting resilient cores 44. This givesthe clinician added flexibility in the design of the prosthesis.Resilient cores can be used in conjunction with precision attachments insituations. where there is heavy occlusal loading (i.e., bruxism,clenching etc.) or when the clinician wants to “bone load” theprosthesis more carefully.

Conclusion.

The development of the spark erosion denture was considered to be animportant step towards creating the ideal implant supported dentureprosthesis. It was machined with exacting tolerances and was patientremovable. However, it did not adequately address the problem of cost,passive fit, screw loosening, hygiene access and excessive cantileverforces.

The SPAD has not only addressed these issues, but at the same time ithas also provided superior esthetics, phonetics, and function.

In a very recent article of the International Journal of Prosthodonticsthe 3 dimensional analyses of one piece implant supported prostheses wasanalyzed. In this article, multiple references were made to frequentframework fracture and how changes in framework designs have “led to anincrease in cross-sectional areas at the junction of the cantileveredregions.” K. B. Tan, J. E. Rubenstein, J. I. Nicholls, R. A. Yuodelis,Three Dimensional Analysis of the Casting Accuracyof One-PieceOsseointegrated Implant Retained Prostheses, 6 Int'l J. ofProsthodontics 346-63 (No. 4, 1993). In fact this article stated that“All authors concur . . . that bulk is needed occlusogingivally in thesection distal to the distal most abutment to provide the requiredstrength for support of the cantilever sections”.

It is the inventor's opinion that the fundamental design of the ad modumBranemark cantilevered frame is outdated. The Zarb study reinforces thispoint due to the large number of component failures it cites. B. D.Monteith, Minimizing Biomechanical Overload In Implant Prostheses: AComputerized Aid To Design, 69 J. of Prosthetic Dentistry (No. 5, May1993). These framework designs need to be reworked because some of themost well respected implantologists such as Jeut, Worthington, Skalak,Carlsson, Jones, Sullivan, and Zarb, all agree that the “inherentdistortions in the existing prosthesis are a possible cause of componentfailure”. Id. The SPAD, on the other hand is not cantilevered.Furthermore, the fact that the framework is smaller and that it is notscrew retained, means that there is less bulk and less stress in thesystem, which translates into less risk of framework distortion.

Tan et al. describe this phenomena by stating, “Potential distortion ofimplant frameworks may be complex and may be magnified by both therelatively large mass of alloy cast and the configuration of theprosthetic framework.” K. B. Tan, et al., supra.

Another fundamental design flaw that these authors point out is thepotential vertical gap and bending moment created between-the frameworkand the abutment cylinders as the result of screw tightening. Thisrotational displacement creates pre stress in the system which makes theprosthesis more prone to failure especially by long term fatigue.

Other design limitations of these cantilevered frames include screwloosening, and screw fracture—problems that have already been mentioned.

The SPAD on the other hand does not have these design limitations.

The following is a brief review of what makes SPAD so unique:

1. It uses resin bonding technology and intra abutment precision slideattachments to solve the problem of passive fit and patientremovability.

2. Due to the unique design of the UAS and MUAS abutments, the SPAD hasan anti-screw loosening capability.

3. The stressbreaking attachments that are housed in the framework andthe denture saddles provide for a more even distribution of occlusalforces and stressbraking.

4. Because the framework is not held to the abutments by screws there islimited rotational displacement or pre stress tendency in the system.

5. The stress broken extensions, in a bilateral situation, have nolingual bar and are removed as a single component along with the rest ofthe prosthesis.

6. The entire prosthesis is patient removable which leaves only theindividual abutments to clean around and no connecting tissue bar.

7. The retention of the prosthesis is adjustable.

8. Both the abutments and the framework can be made in Titanium and aretherefore totally biocompatible.

9. It uses a minimum number of components and only 4 implants.

10. The abutments can be fabricated using CAD/CAM technology.

11. Modified resilient core assemblies can be used during progressivebone loading or to help cushion heavy occlusal forces in a bruxer orclencher.

Part 4: Patient Removable Intra Abutment Precision Attachment Crown andBridge Assemblies for the Edentulous and Partially Edentulous Patient.

Abstract.

Intra abutment precision slide attachment crown and bridge assemblieshave many advantages over the existing prosthetic appliances. Insituations where only minimum cantilevers are required due to adequateimplant placement, these new prostheses offer better aesthetics and morecomfort and stability than the removable metal/acrylic denture systems.Perhaps the biggest advantage that these systems have over the screw orcementable crown and bridge appliances is daily patient removability,which creates better periodontal maintenance and more leeway toovercontour ridge laps and over-extend the porcelain and metal. Thisability helps compensate for problems associated with ridge resorption,implant angulation and lack of interdental papillae, problem for whichexisting technology and prosthetic designs have limited solutions.

Even with all the advantages that these precision attachment assemblyoffer, without UAS or MUAS abutments of the present invention, theproblems of passive fit and screw loosening cannot be solved, and theprecision attachments cannot be mounted within normal abutment contourseven with telescopic copings.

The solutions to these problems will also be detailed below during thediscussion of patient removable intra abutment precision attachmentprostheses using abutments of the present invention. An intra abutmentprecision attachment alternative using abutments of the presentinvention is also disclosed for a partially edentulous situation to helpillustrate the flexibility of this prosthetic concept.

Introduction.

The following discloses a technique that almost completely eliminatesthe risk of peri implantitis (except that, perhaps, caused by occlusaloverloading) in a patient who has undergone the complete restoration ofthe maxillary arch with six implants using standard abutments and aunique patient removable crown and bridge prosthesis. This prosthesiswill later be compared to a model according to the present invention.

The screw retained implant bridge is considered by many to be thequintessence of full arch implant supported restorations. However, inthe inventor's opinion, the screw retained fixed bridge has severelimitations because, among other things, it cannot be removed by thepatient and therefore the peri implant tissues cannot be readilycleaned. U. Grunder, J. R. Strub, Implant-Supported SulrastructureDesign, 10 Int'l J. of Periodontics and Restorative Dentistry 18-38 (No.1, 1990); D. E. Tolman, W. R. Laney, Tissue-Intergrated ProsthesisComplications, 7 Int'l J. of Oral and Maxillofacial Implants 477-84 (No.44, 1992); R. B. Johns, et al., A Multicenter Study of OverdenturesSupported by Branemark Implants; R. P. Desjardens, Prosthesis Design forOsseointegrated Implants in the Edentulous Maxilla, 7 Int'l J. of Oraland Maxillofacial Implants 311-20 (No. 3, 1992); B. Langer, D. Y.Sullivan, Oassointegration: Its Impact on the Interrelationship ofPeriodontics and Restorative Dentistry: Part II; 9 Int'l J. ofPeriodontics and Restorative Dentistry 165-83 (No. 3, 1989); G. J.Chicho, et al., Adapting Fixed Prosthodontics Principles toScrew-Retained Restorations, 2 Int'l J. of Prosthodontics 317-412 (No.4, 1989); G. J. Chiche, A. Pinault, Consideration for Fabrication ofImplant Supported Posterior Restorations, 4 Int'l J. of Prosthodontics37-44 (No. 1, 1991); R. M. Watson, D. M. Davis, G. H. Forman, T. Coward,Consideration in Design and Fabrication of Maxillary Implant SupportedProstheses, 4 Int'l J. of Prosthodontics 232-39 (No. 3, 1991); K. B.Tan, J. E. Rubenstein, J. I. Nicholls, R. A. Yuodelis, Three-DimensionalAnalysis of the rastina Accuracy of One Piece, OsseointegratedImplant-Retained Prostheses, 6 Int'l J. of Prosthodontics 346-63 (No. 4,1993); M. Perel, Retrievability and Screw-Hole Access, 4 DentalImplantology Update 55 (FIG. 9), 60 (FIGS. 5-10) (No. 8, 1993); M.Perel, Interview with Y. M. Ismail: Occlusion and Biomechanics inImplant Dentistry, 4 Dental Implantology Update 6-8 (No. 1, 1993); G. J.Christensen, Implant Prosthodontics Contribute to Restorative Dentistry,121 J.A.D.A. 340-50 (September 1990); A. Fenton, The Role of DentalImplants in the Future, 123 J.A.D.A. 37-42 (January 1992); D. A. Gorber,Implants—The Name of the Game Is Still Maintenance, 12 CompendiumContin. Educ. Dent. 876-86 (No. 12); B. Langer, Dental Implants Used ForPeriodontal Patients, 121 J.A.D.A. 505-08 (October 1990); B. D.Monteith, Minimizing Biomechanical Overload in Implant Prosthesis: AComputerized Aid To Design, 69 J. of Prosthetic Dentistry 495-502 (No.5, 1993); I. Ericsson, U. Lekholm, P. I. Branemark, J. Lindhe, P. O.Glanty, S. Nyman, A clinical Evaluation of Fixed Bridge RestorationSuported by the Combination of Teeth and Osseointegrated TitaniumImplants, 13 J. Clin. Periodontal 307-12 (1986).

When gingival skirts and overextended porcelain are used to correctaesthetic shortcomings, the patient's ability to keep the peri implantsulcus clean is severely hindered. This leads to inadequate periodontalmaintenance and is perhaps the leading cause of peri implantitis.Moreover, if these methods (gingival skirts and overextended porcelain)are not employed, the result is often enlarged embrasure spaces, gaps,improperly placed cervical margins and inadequate lip support. Thisoften creates a less than adequate aesthetic look. Additionally, thescrew retained prosthesis is subject to elastic deformation of thescrews which permits openings to appear between the abutments and theframework. This creates a potential shift in leverage forces and a nonpassive fit which ultimately creates a stress on the implant-boneinterface. B. D. Monteith, Minimizing Biomechanical Overload In ImplantProstheses: A Computerized Aid To Design, 69 J. of Prosthetic Dentistry(No. 5, May, 1993).

The solution to this involves a crown and bridge system which is neitheranchored to the abutments by cement nor by screws but rather by aremovable precision attachment assembly. This assembly not only makes iteasier to clean than the cement or screw retained bridgework, but alsomore aesthetic and more versatile since it can be ridge lapped.Furthermore, it can be designed to be removable without any occlusalscrews or access bores, which means that there is no risk of screwfracture with the precision attachment assembly.

Problems with the Edentulous Ridge (Maxillary).

Clinicians routinely see patients who wear a complete upper denture andhave only their lower anterior teeth. This is a very common situationwhich often creates a Pseudo Class III occlusion. Clinically this inturn creates a need to angle the implants at a very steep incline to theocclusal plane, often out of alignment with other implants. This factorin conjunction with the buccal plate resorption pattern of the maxillaryridge creates some very challenging clinical situations. Bony defectsand thin narrow ridges further complicate full arch implant treatment.Later on the inventor will detail how blade implants can be modified toaccept MUAS and UAS (see Section X). Blade implants are used insituations where there are thin, narrow ridges and not enoughsurrounding bone for root form implants.

To compensate for facial ridge resorption in the edentulous jaw theclinician frequently must overcontour the prosthesis to maintain thecorrect lip and soft tissue profile. This overcontouring makes cleansingof the peri implant sulcus extremely difficult. Although this sort ofsituation is usually a very good indication for an overdenture with aflange, it is sometimes difficult to cleanse around the tissue bar. Thetissue bar itself can also cause problems with a bulky palate if it israised off the tissue, and always has the potential problem of screwloosening. The obvious solution to these problems is to design a patientremovable prosthesis with individual abutments to give the patientmaximum comfort and access. Given the choice between a crown and bridgeprosthesis and a denture, most patients would prefer the natural feel ofthe crown and bridgework. In situations where finances are the limitingfactor, fewer implants and an overdenture system is a viable option.However, the tissue bars must be redesigned to deal with the problems ofscrew loosening and passive fit [see this section Part 6 (OverdentureApplications)].

The Disadvatages of Screw Retained Implant Supported Bridgework.

Keeping the screw retained bridgework clean and plaque free isproblematic. M. L. Perel, Interview With H. I. Bader: How To Motivate,Inform Dental Implant Patients On Home Care, 4 Dental ImplantologyUpdate 57-60 (No. 7, 1993). These appliances are designed either with(1) a ridge lap configuration, (2) open embrasures or less frequently as(3) a high water design. All these designs have limitations: The highwater design, for example, where none of the appliance touches thetissue except the abutment sleeves, causes problems with speecharticulation and phonetics (especially fricative and sibilant sounds) asair passes readily under the appliance. Aesthetically, this space is notvery appealing. There is also the problem of patient comfort. For thepatient, a space between the tissue and the appliance is annoying to thetongue. Even if the patient can endure all these problems, the fixedhigh water design still does not allow the patient to readily cleanaround the abutments. The UCLA style bridge with open embrasures sharessimilar problems. Even though the tapers for the crowns start just abovethe neck of the implants the tissue cannot be expanded to create normalsoft tissue contours which leaves rather unaesthetic interproximalembrasures. Once again the UCLA abutments are not patient removable sothe prosthesis is fixed in the patient's mouth and these open embrasuresare required to provide periodontal access.

Frequently, nonparallel implant abutments create situations that leavethe implant collars and sleeves exposed. The only non-surgical way ofdealing with this problem is to overcontour and overextend the porcelainand metal. Since most patients expect an aesthetically pleasing result,overcontouring and ridgelapping the porcelain and metal to hide thesenecks has become more predominant. However, the overcontoured porcelainoften smothers the peri implant sulcus making it virtually impossible toclean.

In order to provide the ideal embrasure spaces, the mesial distal widthof the abutment teeth must be wider as they emerge from the tissue. Forthe screw retained bridge this once again means creating a “ledge” ofporcelain to compensate for this discrepancy. The same situation occurseven more frequently in a buccal/lingual direction where on the labialaspect, the porcelain is often extended up onto the ridge beyond theperi implant sulcus to create the proper cervical margin placement, lipsupport and emergence profile.

From the lingual or palatal aspect improper emergence profiles oftenexist due mostly to the narrow cervical neck area of the implantabutment assembly. When the contours of the transmucosal collar arefollowed or even when direct abutments are contoured, large spaces arecreated which not only serve as a food trap but also feel foreign to thepatients tongue. There is no simple solution to this problem, becausecreating an overhang of metal or porcelain with a screw retainedprosthesis to accurately reproduce the normal emergence profile of thenatural teeth would make it almost impossible to clean.

As mentioned earlier, at least one supplier, 3I, has attempted to solvethis problem by tapering the tissue using new tapered healing collars.As discussed immediately below, the screw retained prostheses whichreplace these tapered healing collars rattle loose. Therefore, it is notenough to simply taper the tissue, for frequently the prostheses have tobe overcontoured. The solution is to eliminate the screws and make theprosthesis patient removable. At

At an implant symposium (September 1993) in New York USA when the topicof discussion was confined to implant failures, Dr. Carl Misch wasquoted as saying, “Screws rattle loose.” (Indirect VerbalCommunication.) This is true, but not only do they come looe, they alsofracture. This fracturing, which has been reported repeatedly in theliterature, is due to biomechanical overload which frequently causes theweakest link in the system to break. In the inventor's opinion, to havescrews fracturing as a normal event is no way to maintain patientconfidence or deal with the problem of bio shanical overload. As justmentioned, the solution is to simply design a retrievable system thatdoes not have gold alloy screws and a system that has shorter strongerfixation screws. It must be remembered that once the fixation screwbreaks the prothesis is no longer passive fitting.

One final problem with this type of prosthesis is the incorporation ofscrew-joint prestress which occura when the screws are used to tightendown the framework. Tan et al. summed it up by saying, “Tightening theprosthesis onto the intraoral abutments may make the framework appear tofit, but may hide the existence of a prestress within the components andframework induced by this screw tightening. The superimposition offractional stress (e.g., from mastication) upon this prestress will makethe prosthesis more prone to failure, especially by long-term fatigue.”K. B. Tan, J. E. Rubenstein, J. I. Nicholls, R. A. Yuodelis, ThreeDimensional Analvsis of the Casting Accuracy of One-PieceOsseointegrated Implant-Retained Prostheses, 6 Int'l J. ofProsthodontics 346-63 (No. 4, 1993).

The Precision attachment Assembly Using Existing Technology.

This prosthesis illustrates the benefits of precision attachmentremovable assemblies, but also makes the point that limitations imposedon this case by conventional abutment systems can be corrected if UAS orMUAS technology is incorporated.

Assuming that the patient has an adequate number of implants to carrythe load of an implant-supported prosthesis, most patients when giventhe choice, would prefer the crown and bridge prostheses to theoverdentures. However, the periodontal maintenance that the patientremovable systems offer is a very big plus. To have the feel of fixedcrown and bridge that is able to be removed on a daily basis would beideal.

The following case report details the use of such a system. Even thoughhardware according to the present invention was not used for reasonsjust discussed, the purpose of this clinical case was twofold: (1) toshow the benefits of precision attachment assemblies and (2) to helpclinicians realize the limitations imposed on this case by usingexisting technology. These problems and shortcomings will be disclosedas will an alternate solution using a working prototype model. onceagain a clinical case can be organized for further demonstrationpurposes.

A 53 year old female wore a complete upper denture and complained thatit had never fitted correctly. The patient also wore a cast partiallower denture but wanted really to rid herself of both dentures and wasinterested in implants. After consultation with an oral surgeon it wasdetermined that she was a good candidate for implants.

The treatment plan called for the placement of a precision attachmentremovable crown and bridge prosthesis supported by at least 6 endostealimplants.

In March 1990, six Dentsply HA coated microvents were placed in themaxillary arch. They were of varying diameters but all were between10-13 mm in length. There were at least three sites that proved to beunacceptable because the bone was either too soft or the maxillaryplates were too knife edged and this led to perforation. Thus, only twoimplants were able to be placed in the upper left quadrant. In hindsightthis may have proved to be an excellent site for a blade form implant.If the surgeon had the opportunity to retreat this case in 1993 either ablade form implant would have been placed or bone augmentation and atissue guided regenerative procedure would have been undertaken to treatthe upper left quadrant.

In September 1990, the six maxillary implants were uncovered using afull arch mucoperiosteal flap, and healing collars were placed. However,during the healing period on several occasions the collars came loosecreating tissue ingrowth between them and a subsequent “foul odor.” Tocorrect this problem the collars were removed, the tissue tags wereremoved and the healing collars were screwed back to place with Biosealcoated on the screw threads.

In early November 1990 a combination of conventional angled titaniumabutments and hex lock abutment analogues were placed to assess theposition and axial inclination of the implants. Because of anatomicaland surgical limitations several of the implants were placed at rathersevere angles. Even utilizing 15° and 30° angled titanium abutments,“draw” could not be achieved in a conventional manner, even afteraggressively grinding down the abutments. As a result, gold telescopiccopings had to be fabricated overtop of these abutments to align all siximplants. Oval shaped openings were made in the facings of these copingsthat lined up with the screw holes in the HLAs and ATAs allowing forabutment retrievability. This unfortunately also created a problem withscrew loosening. Before the copings were cemented into place (which alsocreated some concern) the patient removable crown and bridge frameworkhad to be fabricated.

Four KSG Audax precision slide attachments were used. The matrixcomponents were cast as part of the gold telescopic copings on thedistal aspect of abutments #15, 14, 23 & 25. This was an exceedinglydifficult task for not only did “casting to” put the attachments under agreat deal of temperature stress but, because of the abutments' centralaccess bore design, the attachments had to be mounted well outside thecentral long axis of the implant. Trying to minimize the lateralstresses that this created by altering the abutments proved to bevirtually impossible.

Once the copings were tried in and were fitting precisely, they werecemented permanently to the abutments. A palladium-gold crown and bridgeframework was made then to extend from #16-#26. On the internal aspectof the crowns for teeth 15, 14, 23 & 25 the patrix components of the KSGattachment had been cast. The fitting of the framework and the castingof the attachments created a strong concern over passive fit. Withoutbeing able to utilize the technology of the present invention,confirming a passive fit was impossible. In fact the extra filmthickness of the cement used to cement the copings was enough to disruptthe alignment of one attachment and then the entire case. Rather thantrying to remove the coping from the abutment, the patrix component inthe framework was carefully cut out and the framework was relieved. Thepatrix component was then fully seated back into the matrix and a pickup impression was taken with the framework in place. The lab used thisimpression to index the position of the patrix and then resolder it.This was a very complicated, time consuming endeavor but the prosthesisdid finally fit. Four small threaded screw holes were used to check theinternal fit of the framework and make sure that it was seating evenlyon the copings and not being held up by a misaligned precisionattachment.

The framework was extended outward covering the palatal tissue and wascreated to butt joint the palate in order carefully to duplicate theemergence profile and contour of the natural dentition.

Under normal circumstances, such as with a screw retained or cementablebridge, this could not have been done simply because the patient wouldhave been unable to keep the area clean. Since the patient could removeand clean the precision attachment appliance daily, however, thisovercontouring of the framework was possible. As the porcelain wasapplied to the framework it too was extended labially, palatally andinterproximally out over the peri implant sulcus. These phonetic andaesthetic advantages cannot be achieved unless the clinician is preparedto ridge lap the tissue and overextend the porcelain. Without thesecontours proper lip support could also not have been achieved with acrown and bridge prosthesis.

Two bisque bake try ins were completed to finalize the occlusal schemeand the final contour of the prosthesis. However, due to the bulk of theHLAs and ATAs and the added bulk of the telescopic copings, by the timeporcelain was added to the framework the incisal-lingual contours of theprosthesis were too bulky. This “bulkiness” interfered with thepatient's speech. The finished appliance was then given to the patientwho was instructed to wear it at all times but to remove it twice dailyto clean around the copings and the underside of the prosthesis. Thepatient was instructed to clean with a combination of a Hydroflossmachine and a Rotadent toothbrush. As an adjunct, the patient has foundthat by looping superfloss around the copings and crisscrossing thefloss she can maneuver it into the peri implant sulcus which needscareful cleaning. occasionally the patient develops an odor problem asbacteria get trapped in the occlusal access bore.

The patient has had absolutely no problem removing the prosthesis on adaily basis and has stated that “the appliance feels as if it were fixedinto place.” Implants associated with overdentures cannot claim thissame stability. However, they can claim to be more accessible than theirscrew retained or cementable crown and bridge counterparts. By the sametoken, this patient removable precision attachment prosthesis allows foreven better access to the implant abutments because there is no tissuebar. Complete and unrestricted 360° access allows for unbeatableperiodontal cleansing. This is perhaps one of the most important aspectsof this technique, one which is carried over to the design of thepresent invention.

Conclusion.

The unique design of this precision attachment system that allows it tobe removed on a daily basis not only permits more predictable home carebut also circumvents the need to use set screws to anchor thesuperstructure. For this reason there are no screws that perforate theexternal surface of the crown and bridge assembly.

As already pointed out when eccentric screw positions are created,destructive lateral forces and stresses on the prosthesis lead to“retrograde peri implantitis” which occurs due to uicrofracturing in thebones With a precision attachment assembly such as this one the problemsassociated with eccentric screw position are eliinated.

A great deal of work has gone into circumventing the aesthetic problemsassociated with the partially or completely edentulous ridge. Forexample, when proper gingival labial contours cannot be achieved due toimplant position or tissue defects, bone grafts or tissue guidedregeneration procedures may be, used in partially edentulous cases.However for the completely edentulous maxillary ridge, where resorptionis often moderate to severe and is more generalized, these alternativesare not completely successful due to resorption and slumping. Ridgeaugmentation in situations such as this usually involve significantautogenous bone grafts from either the iliac crest or symphysis area.For most people major reconstructive surgery such as this is not apractical solution.

Improper implant position creates other problems as well, including pathof insertion problems, eccentric screw positions, and aesthetic andocclusal discrepancies. With the introduction of the pre angledabutments some of these problems were magnified. Many people believethat the forces of occlusion being placed on these angled abutments arenot being directed along the vertical axis of the implant fixture.Furthermore, when telescopic copings are used to create a common path ofinsertion among multiple abutments, the margin of the coping oftencreates an aesthetic problem, for they have to be raised occlusally toallow for “draw” with the other abutments. This causes the metal collarof the telescopic coping to show from the labial aspect. This metalcollar cannot be masked unless the PBG crown is overextended andovercontoured. once again this makes cleaning both the tissue and theprosthesis difficult.

Studies have shown that the peri implant sulcus is lined with a sulcularepithelius and more apically with a junctional epithelium. It appearsthat the sulcus is very similar to that of a natural tooth, but withoutthe periodontal ligament. Clinically this is very relevant to therestoration of the edentulous anterior maxillary jaw. Often theoverlying tissue is thin and friable and because the body likes tomaintain a “biologic width” between the crestal bone and the base of theperi implant sulcus, subgingival margin placement is not alwayspossible. When inappropriate prosthetic contours are created to correctfor such problems the periodontal maintenance of such an appliance isput in jeopardy.

One other problem that this thin friable mucosa often creates is a lackof interdental papillae. Even with shorter transmucosal collars thatdiverge more at their junction with the abutment, it is very difficultto get the proper emergence profile and create or simulate interdentalpapillae. The result is once again an aesthetic compromise. Even withmore anatomically correct implant systems the resorption of the ridgecombined with the thin mucosal coverage often makes it impossible toachieve proper aesthetics without overcontouring or overextending theporcelain. overcontouring and overextending truly creates a catch-22situation: Either periodontal maintenance problems or aestheticcompromise.

Periodontal disease is still the leading cause of tooth loss in adultsand now as more and more osseointegrated implants are being placed thecondition known as peri implantitis is becoming more prevalent. It istherefore extremely important that full arch reconstruction allow foradequate cleansing of the peri implant sulcus. The precision attachmentprosthesis is ideally suited for this because the appliance can beremoved daily, with firm bilateral pressure. This allows the patientcomplete access to both the highly polished gold copings and theunderside of the bridgework.

Note that the copings are either supra gingival or level with thegingiva. This prevents any possible encroachment on the biological widthof the connective tissue between junctional epithelium and crestal bone.The collar of the abutment maw show but the porcelain to metalsuprastructure covers it completely, by virtue of its overextendedporcelain margins. This ridge lapping of porcelain, overextending andfilling up the interproximal gaps, only works if the appliance can beremoved daily; otherwise peri implantitis and potential implant loss canoccur.

Overlapping the peri implant sulcus with both the metal framework andthe porcelain is not an acceptable situation on either a cement or screwretained prosthesis for it is imperative that this sulcus be cleaned.Furthermore, the lingual extension of this framework has an emergenceprofile that accurately reproduces that of the natural dentition, unlikethe other prostheses where the lingual surface is usually scooped out.

There are features that cannot be achieved in the edentulous jaw andother crown and bridge systems without severely compromising theperiodontal health of the tissue and patient comfort. For instance, anon parallel abutment requires a telescopic coping which creates avisible metal surface that cannot be covered, without creating anunfavorable overcontour and one which cannot be readily cleaned. Thealternative is either to leave the metal exposed or utilize one of thenew ceramic abutments. Both options allow for cleansibility but arerather unaesthetic.

One final point should be made about those patients who are edentulousand have lost their teeth to periodontal disease. Can a patient such asthis be expected to go from a complete denture to a full arch prosthesisand develop all the necessary habits to keep the appliance clean? If theappliance is screwed or cemented into place this would make itexceedingly difficult, if proper aesthetics are to be maintained. We oweit to these patients to make everything as accessible as possible andthis is why the removable denture systems are so popular. However theiraesthetics and patient comfort are not the best. The solution is aprecision attachment crown and bridge prosthesis which can be removed,to allow for cleaning on a daily basis. at the present time, the onlyother crown and bridge options are cementable or screw retained systemswhich cannot be removed by the patient.

Improving on the Precision attachment Assembly Using USA/MUASTechnology.

Using state of the art conventional abutments, this precision attachmentassembly demonstrated some major limitations. Beside the fact that ithad to use secondary telescopic copings, the most obvious limitation ofthe foregoing system was the use of abutments with central access bores.This creates screw loosening problems and an inability to place theprecision attachment housings within the normal contours of theabutment. This in turn leads to non axial loading of the implant boneinterface and can create destructive lateral forces that can lead toretrograde peri implantitis.

Had the UAS/MUAS system been used in this particular case, there wouldnot have been a need to fabricate telescopic copings. Without thecopings, there would have been no need to use cement to join them to theabutments and risk altering the attachments' position (which did in facthappen). In fact, fewer parts would have been necessary without thecopings and there would not have been the problems associated with acentral access bore.

The hours and hours that were spent aligning the hex and octagonposition of these abutments, every time the abutments were tied in, werealso wasted time. This could have been avoided if UAS or MUAS threadedbase 10 assemblies were used. There are also clinicians who believe thatone does not need anti-rotational abutments for bridgework; however thisis simply not true, when the present invention is used. In order toalign two or more precision attachments accurately, the exact rotationalposition of the abutments mist be reproduced. The problem in assemblingprecision attachment prostheses with existing abutments that do haveanti-rotational capabilities is that there are simply too manyhex-octagon or other mechanical interlocking combinations. For manyabutments, these multiple rotational positions are a key sellingfeature, which is fine if is the clinician needs only to align one ortwo abutments. For five or six, however, the potential number ofrotational positions for a commonly used ATA is 24⁶ or 191,000,000!

With the MMAS/UAS System one of these interlocks is eliminated and isreplaced with a threaded component, which reduces the number ofrotational positions for each abutment to 6 or 8 depending on theindividual system. Needless to say, the potential number of rotationalpositions is greatly reduced.

For the patient mentioned above, although there were no secondary setscrews to fracture or loosen, several of the main fixation screws didwork themselves loose. This could have been avoided had a UAS/MUASSystem been used. It is this author's opinion that screw loosening is avery good indication of a non passive fitting prosthesis; in this caseit is highly likely that it was a non passive fitting framework thatcaused the fixation screws to loosen.

The “bulky” aesthetic problem with the prosthesis, which is due to theaccess bore holes and the extra thickness required for the copings,ceases to be a problem with the present invention. Neither the accessbore holes or the copings are needed and therefore the abutments can bemade slimmer and more compact. As a result, so can the crown contours.This also helps solve the problem of speech articulation discussedearlier.

Another major limitation with this conventional system has to do withpassive fit. In the inventor's opinion, any system that has centralaccess bores and screw loosening potential has a problem with passivefit because, as soon as the screws loosen, the abutments are not beingloaded in the same manner. This is what frequently leads to screwbreakage and likely why the Branemark system screws are designed tobreak. The present invention, by contrast, simply eliminates allocclusal screws and thus eliminates risk of loosening or breakage.

The problem of passive fit also has to do with the fact that precisionattachments for this conventional prosthesis are cast to place in thelab which creates a potential source of distortion. The conventionalabutments are not designed to allow for intra abutment resin bonding ofattachments—without which a passive fit cannot be achieved.

Upon examination of the prototype models of this specific case, itbecomes very apparent that use of UAS or MUAS abutments would reduce oreliminate all of the problems associated with this precision attachmentassembly.

It should also be noted that the framework is made of titanium which isapproximately one quarter the weight of the original prosthesis.Individual crowns or sections of crowns can also be telescoped on theframework and lingually set screwed to position. Telescoping crowns inthis manner serve two purposes: (1) so that damage to one section of thecrown or crowns does not require refiring of the entire bridge or any ofthe attachments; and (2) if vertex attachments according to the presentinvention are used the clinician needs to be able to access the occlusalspreader screws to adjust the tension on the attachments.

Fabricating Precision Attachment Assemblies with Resilient Cores usingModified USA/MUAS Technology.

Careful attention must still be paid to prevent overloading the implantbone interface especially in patients with heavy occlusal function(i.e., bruxism and clenching). Normally this is done by narrowing theocclusal table, removing damaging lateral forces of occlusion andpremature contacts. However in many instances this is not enough,especially during the first year the appliance is being worn when theimplant-bone interface is still maturing. The IMZ suppliers recommendthat an intramobile element (IME) made of polyoxymethylene be used as ashock absorber. This is an excellent idea as; stress distribution, shockabsorption and proprioception are all said to be facilitated by the useof an IME.

Unfortunately the utility of the IME of the IMZ system is limitedbecause of potential screw loosening problems, access bore location, ahigh percentage of IME breakage and the fact that the overlyingprosthesis cannot be made precision attachment patient removable. M. L.Perel, Interview With Dr. H. J. Gulbransen: Combining Implants andNatural Teeth Within the Same Arch, 4 Dental Implantology Update 74-76;(No. 9, 1993); R. C. Hertel, W. Kalk, Influence of the Dimension ofImplant Superstructure on Peri-Implant Bone Loss, 6 Int'l J. ofProsthodontics (No. 1, 1993); E. A. McGlumphy, W. V. Campagni, L. J.Peterson, A Comparison of the Stress Transfer Characteristics of aDental Implant with a Rigid or a Resilient Internal Element, 62 J. ofProsthetic Dentistry 586-93 (No. 5, 1989); D. C. Holmes, W. R. Grigsby,V. K. Goel, J. C. Keller, Comparison of Stress Transmission in the IMZImplant System with Polyoxymethylene or Titanium Intramobile Element: AFinite Element Stress Analysis, 7 Int'l J. Oral Maxillofacial Implants450-58 (No. 44, 1992); R. K. K. Ow, K. H. Ho, Retrieval of the ResilientElement in an Osseointegrated Implant System, 68 J. Prosthetic Dentistry93-95 (July 1992). As an example of this, IME's could not be used inconjunction with the previously discussed prosthesis because theconventional abutments could not be made compatible with the IME.

Therefore it is obvious that a system such as the UAS/MUAS whoseresilient core does not cause all of these problems and is universallycompatible would be perfectly suited for this purpose. Not only can suchModified UAS/MUAS Assemblies be used to help absorb excessive occlusalloading, but they can also be used to help progressively bone load theprosthesis. One of the biggest differences between the DKM and theresilient core is that the resilient cores can easily be removed andreplaced without disturbing the threaded base 10-implant connection orfixation screw. This is not possible with the IMZ system; additionally,the exact rotational position of the abutment of that system cannot beaccurately duplicated either.

Furthermore, because of the IME's central access bore and fixationscrew, there are some critics who believe that it is the bending momentexerted on the elongated fixation screw that accounts for this system'sresiliency. Unfortunately, this puts a great deal of stress and strainon the screw itself and is considered to be the reason why the screwsloosen and fracture.

With the resilient core system of the present invention, there is nocentral access bore or elongated fixation screw. Accordingly, inaddition to solving these problems, this feature also allows cavities tobe created within the abutment for precision attachment placement. Theresilient core system can also be readily replaced with a titaniumanalog which duplicates its size and shape exactly. The titanium analogsimply eliminates the “flex” in the system when the clinician feels thata more rigid prosthesis is desirable.

One additional very important advantage that the resilient core enjoys,because it fits solidly onto the threaded base 10 portion of theModified UAS/MUAS System, is that it is adapted to function with anyimplant system including blade form implants. The IMZ system does nothave this sort of “flexibility.”

An Alternative Solution for the Partially Edentulous Situation.

A recently featured article in the “Journal of Oral and MaxillofacialImplants” by Svensson et al. described bow the position of fourmisaligned Branemark implants was corrected by a segmental osteotomyprocedure. B. Svensson, R. Adell, B. Swarte, Correction of ImplantMalalignment by Segmental Osteotomy: A Case Report, 8 Int'l J. of Oraland Maxillofacial Implants 459-63 (No. 4, 1993). This procedure was usedbecause the initial palatal placement of the fixtures resulted inphonetic and hygiene problems for the patient. In fact, “the patientcould not tolerate the prosthesis because of phonetic problems (lisping)and inadequate tongue space.” She also “spent a disproportionately longtime every day trying to gain access to And clean her implantabutments.” Id. The article further states that it was the Buccalextension of the prosthesis that resulted in the hygiene access problem.If a precision attachment patient removable prosthesis according to thepresent invention had been initially fabricated, the inventor believesthat significantly less time would have been required for optimum oralhygiene and superior aesthetics and phonetics. The only concern leftwith the original prosthesis would then have been to create the properdentoalveolar relationships with a rigidly cantilevered prosthesis. Forthis reason, the inventor concurs with Svensson et al. that thesegmental osteotomy was the correct treatment, although not with thechoice of the final prosthesis.

After the osteotomy procedure was performed a similar prosthesis wasfabricated. However this time it “did not intrude on palatal space” orhave such an “extensive Buccal Flange.” It did, however, remain screwretained, the access bore holes were still covered over with a temporarycement and the necks of the implants were still left exposed.

The final prosthesis could just as easily have been made precisionattachment patient removable which would have allowed more ridge lappingand far better hygiene access to the individual abutments. The ridgelapping would have allowed for better aesthetics and would have reducedthe passage of air above the prothesis.

The use of precision attachment assemblies in similar situations wherethe prosthesis is either screwed or cemented to place can be readilyshown to improve on both form and function.

Part 5: Dealing with the Problem of Combined lmplant-tooth Restorations.

There is a great deal of controversy regarding prosthesis design and thecombined implant-tooth restoration. However, most people will agree thatimplants are most frequently joined to natural teeth to lend extrasupport and redistribute the occlusal load in situations where thenatural dentition is diminished or shows signs of increased mobility.

Many clinicians endorse the use of Boos type attachments (semi precisiontube and lock) to connect the tooth—and fixture-supported segments ofcombined implant-tooth bridgework. I. Ericsson, U. Lekholm, P.Branemark, J. Lindhe, P. Glantz, S. Nyman, A Clinical Evaluation ofFixed Bridae Restorations Supported by the Combination of Teeth andOsseointegrated Titanium Implants, 13 J. Clin. Periodontal 307-12 (No.4, 1986). Unfortunately the tooth segment adjacent to this attachmentfrequently becomes intruded leaving the paternal part of the attachmentprotruding. Furthermore, pronounced bone loss can often be seen aroundthe implant abutments when this type of interconnection is used. It isthe inventor's opinion that when semiprecision attachments and other nonrigid connectors are used they do not provide adequate splinting formobile teeth. Furthermore, any amount of freedom in the attachmentsactually increases the “cantilever effect” to the implant abutment(essentially the intruded teeth become cantilevers). This canundoubtedly lead to an overload of the implant bone interface and resultin bone loss. In the Ericsson article this is exactly what they foundclinically, “pronounced bone loss around the fixture abutments.” Id.

There are other clinicians who feel that implant supported teeth shouldbe isolated from natural teeth in the partially edentulous patient;however, when the implants are isolated, a greater number ofcomplications often arise. These include: (a) component fracture; (b) ahigher incidence of loose screws; (c) difficulty in equilibrating theocclusion; and (d) implant failure.

On the other hand, there are those who feel that one can cautiouslyconnect teeth to implants in a fixed/fixed manner and others that feelthis should be done with intra-coronal semi-precision attachments asEricsson and others have detailed. Still others feel that rigid screwretention of the components is the solution but this has proven to leadto idiopathic bone loss around the implant. Perhaps the most plausibleapproach to date has been offered by Dr. Howard Kay as follows. Let ustake, for example, the almost completely edentulous arch, save 3 or 4natural teeth. Kay's recent article points out that when the clinicianis joining implant and natural teeth together, the use of intra mobileelements seems to enjoy “the highest level and largest number of overalllong-term reported implant success.” H. B. Kay, Free Standing VersusImplant-Tooth Interconnected Restoration: Understanding theProsthodontic Perspective, 13 Int'l J. of Periodontics and RestorativeDentistry (No. 1, 1993). It seems that, as Kay points out, thesemi-precision attachments, i.e. tube locks, “are inherently unstableand display the potential for migration of natural tooth segments”. Id.Furthermore, Kay adds that the use of rigid tooth-implant connectionscan lead to “unexplained bone loss around implants.” Id. Theseconclusions were reached based on the results of over 5,000 toothimplant cases using IMZ implants.

The basic concept behind the IME is that it is made of polyoxymethylenewhich can absorb and distribute occlusal stress to the implant boneinterface more evenly than metal to metal components. In effect the IMEsimulates the periodontal ligament for the osseointegrated implant andeffectively reduces or eliminates any discrepancy in mobility patternsbetween natural tooth and implant abutments.

Many studies, however, have questioned the IME's ability to reduce thetransmission of occlusal forces. One clinician found that these stresseswere not reduced when the IME was used and that maximum stressconcentrations were located in the fastening screw. Others havepostulated that the resin element could protect the screw from fatigueat the top of the implant, but that movement of the screw within the IMEmay also explain the reported, but undocumented, tendency of the screwto “back out” on an occlusal direction.

It is evident from the literature that there are conflicting reports asto the efficacy of the IME. Although the inventor questions the use ofIME's because they can break and for other design reasons, he shares thephilosophy of incorporating resilient connections into implants. Onesolution: Design a system that (1) does not have the same stress placedon its elongated central fixation screw; (2) can be removed and replacedwithout disturbing the rotational stability of the prosthesis; and (3)has no occlusal access or tendency for the screw to back out.

By making these three changes to the resilient component, one arrives atthe Resilient Core UAS or MUAS abutment. There is; also one other veryimportant distinction to be made, and that has to do with the waycertain clinicians choose to restore these combined implant-tooth cases.By incorporating IMEs they limit the prosthetic design. They endorse theuse of dentist retrievable screw fixtures such as the T Block and CSRattachment. T Block structures are used to help reconstruct themaxillary arch in segmented screw retained sections. The remainingnatural teeth are splinted and cemented. CSR Attachments are used tosplint natural teeth and implants together in the lower arch, butfeature numerous screw holes. The final result is often a full archappliance that has ridge lapped prosthetic abutments which cannot beremoved other than by a dentist. As consequence of these designs, thepatients must carefully floss anteriorally where the crowns and ponticsfrequently make contact with the tissue but are “scooped out” linguallyfor hygienic access. Posteriorally, increased spaces must be created toallow for better toothbrush access.

When IMEs are used anteriorally this creates further aesthetic problems.IMEs are placed so that they are exposed above the gum line; theirconstricted diameter renders it almost impossible to create normalanatomical contour without ridge lapping the tissue. In the inventor'sopinion these sorts of nonpatient removable reconstructions make itexceedingly difficult for the patients to clean their mouthsefficiently, to say nothing of the potential phonetic, aesthetic andscrew loosening problems.

When clinicians use the IMZ system, occlusal access bores are difficultto eliminate. In single tooth implant applications, if there are evenminor angulation discrepancies, then telescopic copings must be used toprevent the large access bore holes from opening onto the labial surfaceof the teeth. Other problems include, as Kay himself has stated, “withfreestanding ceramountal restorations . . . I have experienced anunquestionably higher incidence of problems associated with looseningand breakage of fastening screws, breakage of abutment screws and intramobile element failure of implants and in one case breakage ofimplants.” Id.

The present invention offers a unique range of prosthetic options. FIGS.35 and 36 compare, for example, a bridge 82 fashioned according to thepresent invention with a conventional bridge. This bridge is securedconventionally to a prepared natural tooth and a conventional IMZimplant and abutment which features an occlusal bore. Bridge 82 of thepresent invention, by contrast, is removably attached to the naturaltooth via a precision attachment 28 located on the natural tooth copingand to a Modified UAS featuring a resilient core 44 to replicate theligimentation and mobility of the natural tooth. Note that the ModifiedUAS has no occlusal bore hole.

The following case is another example of such a Precision AttachmentPatient Removable Prosthesis according to the present inventionsupported by a combination of Modified UASs (which feature resilientcores) and natural tooth telescopic copings. This prosthesis can eitherbe made as a segmented bridge or a one piece full arch splint. In eithersituation ridge lapping can be used effectively to “hide” the resilientcores simply because the prosthesis is patient removable.

Consider the following working prototype model fashioned after an actualclinical case. This patient had gold copings placed on all of herremaining natural teeth and their margins were finished ever so slightlybelow the gingival crest. In this particular situation elective rootcanal therapy was performed on five of the remaining natural teeth inorder to create proper resistance form and because prior to thistreatment the teeth had been poorly prepared. Exacting attention todetail began with dense, accurate endodontic fills and precisely fittingcast posts and cored. The gold telescopic copings that were placedovertop of the cast posts and natural teeth were all machine paralleledwith 2-4 degrees axial taper.

From the Passelipse X-ray it was evident that four implants were placedinto the patient's maxillary jaw, two of which were placed (#15 & 26) inconjunction with bilateral sinus augmentations. Also of interest is thatin the anterior implant sites the #12 had inadequate bone around it,requiring that allografted bone and a lamellar strip of bone be used toregenerate the deficient areas. Because this involved replacing bothlabial and palatal bone, primary tissue closure could not be achieved.However, the tissue granulated in nicely over the exposed lamellar stripproviding a good thick band of attached gingival tissue because theLamellar strip was resorbable. (See Section II.)

This is how the patient was left—in a temporary occlusion, and allsubsequent steps have been completed on the prototype working model.

On the prototype working model, the four implant supported teeth are allreconstructed using Modified UAS assemblies. All four abutments haveintra abutment slide precision attachments secured to place using theresin bonding technology of the present invention. The attachments areparalleled to the adjacent telescopic copings using a parallelometer.Other abutment systems cannot position the attachments in this mannerbecause they all have central access bores and the attachments cantherefore only be placed extracoronally. Occasionally, there isinsufficient space between the implant and the natural tooth toaccommodate even an extra coronal cantilevered attachment. With the UASSystem this is not even a concern because all attachments can be placedwithin the abutment, which allows the forces of occlusion to be directedin a more axial direction. This is one of the most outstanding featuresof the UAS/MUAS Systems.

In situations where increased retention is required, the telescopiccopings can be fabricated with either machined grooves, slots or evendimples. The dimples can be engaged by adjustable I.C. plungerattachments which can be resin bonded into the overlying framework.

As discussed earlier, this prosthesis can be segmented or fabricated asone piece. The choice of designs will depend on the individual patientbut a sensible guideline would be to keep the minimum segment size to noless than three units. Basically, the only reason one would want tosegment the prosthesis is to appease the patient's psychological neednot to be without all of their teeth.

The copings on the cuspids also have one added feature, which isprecisely machined dimples that are engaged by adjustable I.C. plungerattachments. The I.C. attachments are housed in resin in the overlyingprecision attachment framework, and are incorporated into the prostheticdesign to enhance retention. This prosthesis can in fact be made in asmany as four sections. Section #1 is th cementable PBG crown fabricatedfor tooth #24 to maintain the vertical dimension. If the rest of thesegments can be fabricated so that at least one implant and one naturaltooth are splinted, it is not necessary to splint the entire archtogether. For example, Section #2 of the segmented framework may be thesix unit anterior bridge that splints four natural teeth and twoimplants together. In order to hide the Modified UAS's the porcelain andmetal of the framework can be ridgelapped. This also helps create fullanatomical contour. Section #2 could be the upper left four unit bridgeand Section #3 could be the upper right three unit bridge.Alternatively, Sections #1 and #3 could be combined as one so that thebridge has only three sections. As long as natural teeth and implantsare splinted it is not necessary to rigidly screw retain the entire archtogether as so may clinicians and manufacturers suggest. If the entireprosthesis is to be fabricated in a one piece horseshoe splint at thevery least it should be patient removable. Once again it too can also beridgelapped to create full anatomical contour and eliminate unsightlyspaces.

When resilient cores according to the present invention are used as apart of UAS or MUAS Assemblies, the implant abutments are able toreplicate the periodontal membrane of the natural teeth. This allows fora much more even distribution of occlusal forces and allows the implantabutments to function similarly to the natural teeth.

In the past, rigid fixation of implant and tooth segments lead to thedevelopment of the “Vital Pontic Theory” whereby plaque and fluid couldaccumulate between a telescopic coping and the overlying framework thatwas rigidly attached to the implant abutment. Since the implant abutmentcould not move, a constant hydrostatic pressure buildup between thecoping and the framework lead to a separation and intrusion of thenatural tooth. This would leave that portion of the framework overtop ofthe natural tooth unsupported and so the tar “Vital Pontic” was coined.Vital pontics cause concern because as the tooth intrudes, the balanceof occlusal forces are taken up by the implant and a cantileveringeffect is created.

The inventor believes that because the implant abutments no longer needbe rigidly attached to the frameworks, they can function just as naturalteeth do. Therefore, for the same reason that patient retrievableprecision attachment bridges work perfectly on natural teeth with norisk of hydrostatic pressure buildup and tooth intrusion, these newprosthetic designs will also work in combination tooth-implantsituations.

Part 6: Overdenture Applications.

For many people, fixed-detachable and now patient removable precisionattachment crown and bridge prostheses are not a viable option due tofinancial limitation. For those people, three or four implants, a castbar design and an overdenture is frequently the better solution.Unfortunately with existing abutments systems there are no can bardesigns that do not have exposed fixation screws. Therefore, with thesedesigns there are still the potential problems associated with screwingdown the bar, passive fit problems and hygienic access to name only afew. M. Perel, An Interview with Charles E. English: The MandibularOverdenture, 4 Dental Implantology Update 9-14 (No. 2, 1993); R. B.Johns, et al., A Multicenter Study of Overdentures Supported byBranemark Implants. However, by incorporating UAS/MUAS technology theseproblems cease to be of concern because these new abutments allow forcertain design modifications. As an example when two implants are placedin the symphysis of the lower jaw and UAS/MUAS abutments are secured toposition two intra abutment precision slide attachments can be resinbonded to place. A new bar design as part of the present invention canthen be fabricated, but with at least three significant differences:

(1) The now design as shown in FIG. 36 incorporates two internallymounted precision attachment patrix components rather than simply holes;(2) because of the slide attachments, the newly developed bar of thispresent invention is now patient removable and (3) because theattachments are resin bonded to position, the cast bar design is passivefitting. With UAS/MUAS technology, there no longer exists the need tocreate bar designs with external screw holes. The actual milledsuprastructure of the cast bar can be as it was before; of almost anydesign and can incorporate any number of retentive devices forcooperation with the inside of the denture. These cast bar modificationscan be incorporated into any overdenture design, using any type ofimplant system using when the UAS/MUAS assemblies are employed.

Such an overdenture system according to the present invention is showncompared to a conventional bar in FIGS. 35 and 36.

Part 7: A New Classification of Implant Prosthetic.

Introduction.

The present invention makes it apparent that a new prostheticclassification for implant dentistry is required. The followingclassification system reflects changes in both abutment and prostheticdesigns by incorporating a new order of precision attachment patientremovable prosthetics.

The ADT Classification.

There are four basic intraoral categories;

(1) Fixed prosthetics;

(2) Patient removable overdentures;

(3) Fixed/retrievable prosthetics; and

(4) Intra Abutment Precision Attachment Patient Removable Prosthetics.

Before we examine these categories individually, clarification must begiven to the following terms as there is much confusion over whatqualifies as “Fixed,” “Removable,” “Fixed/Retrievable” and now“Precision Attachment Patient Removable”. Furthermore, it is importantto clearly distinguish between “Removable” and “Retrievable.”

Is all that is Retrievable, Removable? The inventor does not believe so;instead, he believes that a prosthesis should be referred to as aPatient Removable or Dentist Retrievable device, and that the termshould not be interchangeable.

(1) A Fixed Prosthesis—should refer to a crown and bridge appliance thatis rigidly attached to the implant abutment(s) by a permanent cement. Itis therefore neither removable nor retrievable.

(2) A Patient Removable Overdenture—should refer to acrylic overdenturesystems that anchor to the implant abutments with, or without the use ofa tissue bar. In both situations, these denture systems can be removedby the patient. Acrylic overdenture systems that utilize a tissue barcan incorporate a wide variety of semi precision or precision aattachments to stabilize and aid in the removal of the overdenture.These tissue bars however, are held rigidly to the abutments by fixationscrews and are dentist retrievable only.

(3) Fixed/Retrievable—should refer to an acrylic overdenture or crownand bridge prosthesis that is rigidly attached to the implantabutment(s) and or a combination of implant abutments and natural teeth.These prostheses can be anchored by primary fixation screws, secondaryset screws and or temporary cement (which usually involves the use oftelescopic copings). Fixed/Retrievable prostheses can utilize any numberor variety of screw attachments. These attachments are usually mountedor incorporated into a secondary telescopic structure. These prosthesesare not designed to allow for patient removability. As a consequence ofthis design limitation, these prostheses are usually not ridge lappedand are of a high water design. Frequently, these prostheses are alsorigidly cantilevered.

(4) Intra Abutment Precision Attachment Patient RemovableProsthetics—This is the new classification category, and it can referto:

(a) Acrylic Overdenture Systems—this category basically refers to a newdesign of tissue bars that have no external access screw holes and areanchored to the individual abutments by a wide variety of semi precisionor precision attachments. This makes the tissue bar patient removable.This is not to be confused with the patient removable overdenturecategory where the tissue bars are anchored rigidly to the abutments byfixation screws.

(b) Implant Supported Crown and Bridge Systems—refers to appliances thatare rigidly anchored to implant abutments or a combination of abutmentsand natural teeth in a patient removable fashion. This involves theintra abutment positioning of separable precision slide attachments.This allows the patient to remove the overlying prosthesis and does notrequire a tissue bar.

(c) Combination Crown and Bridge/Acrylic Denture Systems—this categoryrefers specifically to stress broken denture situations where a crownand bridge system requires a hingeable denture saddle to lend tissueborne support in an non-implant bearing area of the mouth.

(d) Combined Implant/Natural Tooth Systems—this category refers toimplant and natural tooth segments that are splinted together withresilient cores and precision slide attachments.

This new category has obvious advantages over the three previouscategories because the prostheses are designed to circumvent theproblems of screw loosening, screw breakage, patient cleansability,passive fit, esthetics, phonetics and axial loading.

The sub-classification of this four categories are as follows:

1. Fixed Prosthetics.

(a) Single tooth implant—cementable (it makes no difference whether theunderlying abutment is retrievable because the overlying crown ispermanently cemented).

(b) Multiple unit implant supported crown and bridge—cementable.

(c) Combined implant/natural teeth crown and bridge—cementable.

2. Patient Removable Overdentures.

(a) simple overdentures;

(b) tissue bar overdenture—with or without a cantilevered bar;

(c) spark erosion overdenture;

(d) HA-TI solder base overdenture;

3. Fixed Retrievable.

(a) ad modem Branemark denture—utilizes rigid cantilever and is screwretained;

(b) implant supported crown and bridge—single tooth crown:

held by primary fixation screw

held by secondary set screw

temporarily cemented

multiple unit crown and bridge

held by primary fixation screws

held by secondary set screws

held by telescopic copings and temporary cement

(c) combined implant/natural tooth crown and bridge retrievable implantcrown segments are joined to fixed natural tooth segments. Theprostheses may or may not incorporate resilient components.

4. Intra Abutment Precision Attachment Patient Removable Prosthetics:

(a) acrylic overdentures—now bar designs according to the presentinvention fall into this category and

(b) implant supported crown and bridge prostheses—these System have noexternal access screw holes.

the precision slide attachments are mounted within that contour of theabutment and the prostheses is patient removable and has no tissue bar.

(c) combined crown and bridge/acrylic denture systems—stress brokendenture

(d) combined implant/natural tooth prostheses—Resilient Cores.

Note that 4 a,b,c can also be fitted with Resilient Cores no matter whattype of implant system is used as long as UAS/MUAS Assemblies areutilized.

Conclusion.

With the technology of the present invention there is no longer any needto place single implant restorations with large access bore holes forthe primary fixation screw. All single crown restorations can now beanchored using a lingually positioned tubs and screw rather thanmanually tapping a thread into the wall of the abutment. Because of theUAS/MUAS design there is also less risk of screw loosening and screwbreakage. Furthermore, fully contoured anatomically correct crowns cannow be created without flapping the periosteum or ridge lapping thetissue.

As far as multiple crown and bridge assemblies are concerned, there arenow alternative anti screw loosening abutments without central accessbores which give rise to an entirely new generation of intra abutmentprecision attachment patient removable prostheses.

With regard to combined implant/tooth restorations, these new abutmentsallow implants and natural teeth to be rigidly splinted together byincorporating resilient core components. The further incorporation ofprecision slide attachments allows this new generation of prostheses tobe made patient removable.

This very same abutment system can also be used to radically alteroverdenture designs as well. The technology of the present inventionalso eliminates problems associated with passive fitting tissue bars andscrew loosening.

Section VIII: Evaluating Precision Attachment Designs for ImplantAbutments

With the very recent advances in implant abutment designs and resinbonding techniques, there is a very real need to re-evaluate precisionattachment designs and applications in implant dentistry. Up until now,precision attachments have played a very minor role in the constructionof an implant fixture. Screw blocks, T Blocks, set screws and simpledovetail and tube and lock slide attachments have been utilized, butwith a very limited application. In fact the vast majority of theseprecision attachments have simply been used to help screw down, secureor tie together single or multiple crown and bridge frameworks so thatthey are held rigidly in place and can only be removed by the clinician.U. Grunder, J. R. Strub, Implant-Supported Suprastructure Design, 10Int'l J. of Periodontics and Restorative Dentistry 18-38 (No. 1, 1990);D. E. Tolman, W. R. Laney, Tissue-Integrated Prosthesis Complications, 7Int'l J. of Oral and Maxillofacial Implants 477-84 (No. 44, 1992); R. B.Johns, et al., A Multicenter Study of Overdentures Supported byBranemark Implants; R. P. Desjardens, Prosthesis Design forOsseointegrated Implants in the Edentulous Maxilla, 7 Int'l J. of Oraland Maxillofacial Implants 311-20 (No. 3, 1992); B. Langer, D. Y.Sullivan, Osseointegration: Its Impact on the Interrelationship ofPeriodontics and Restorative Dentistry: Part II; 9 Int'l J. ofPeriodontics and Restorative Dentistry 165-83 (No. 3, 1989); G. J.Chiche, et al., Adapting Fixed Prosthodontics Princigles toScrew-Retained Restorations, 2 Int'l J. of Prosthodontics 317-412 (No.4, 1989); G. J. Chiche, A. Pinault, Consideration for Fabrication ofImplant Supported Posterior Restorations, 4 Int'l J. of Prosthodontics37-44 (No. 1, 1991); R. M. Watson, D. M. Davis, G. R. Forman, T. Coward,Consideration in Design and Fabrication of Maxillary Implant SupportedProstheses, 4 Int'l J. of Prosthodontics 232-39 (No. 3, 1991); K. B.Tan, J. E. Rubenstein, J. I. Nicholls, R. A. Yuodelis, Three-DimensionalAnalysis of the Casting Accuracy of One Piece, OsseointegratedImplant-Retained Prostheses, 6 Int'l J. of Prosthodontics 346-63 (No. 4,1993); M. Perel, Retrievability and Screw-Hole Access, 4 DentalImplantology Update 55 (FIG. 9), 60 (FIGS. 5-10) (No. 8, 1993); M.Perel, Interview with Y. K. Ismail: Occlusion and Biomechanics inImplant Dentistry, 4 Dental Implantology Update 6-8 (No. 1, 1993); G. J.Christenson, Implant Prosthodontics Contribute to Restorative Dentistry,121 J.A.D.A. 340-50 (September 1990); A. Fenton, The Role of DentalImplants in the Future, 123 J.A.D.A. 37-42 (January 1992); D. A. Gorber,Implants—The Name of the Game Is Still Maintenance, 12 CompendiumContin. Educ. Dent. 876-86 (No. 12); B. Langer, Dental Implants Used ForPeriodontal Patients, 121 J.A.D.A. 505-08 (October 1990); B. D.Monteith, Minimizing Biomechanical Overload in Implant Prosthesis: AComputerized Aid To Design, 69 J. of Prosthetic Dentistry 495-502 (No.5, 1993); I. Ericsson, U. Lekholm, P. I. Branemark, J. Lindhe, P. O.Glanty, S. Nyman, A Clinical Evaluation of Fixed Bridge RestorationSupported by the Combination of Teeth and Osseointegrated TitaniumImplants, 13 J. Clin. Periodontal 307-12 (1986).

However, with the UAS and MUAS designs, which eliminate the centralaccess bores in the abutments, cavities for intra abutment precisionslide attachments which can be resin bonded to place can now be created.This allows a new generation of crown and bridge frameworks to be madedetachable and patient removable. These designs permit an entirely newset of design parameters and attachments to be created in order todevelop stress broken prostheses, eliminate problems of passive fit andrender the patient removable appliances user friendly.

Most precision attachments are made of metals and designed to be cast toor soldered rather than resin bonded. However Cendres & Metaux isbreaking new ground in this respect but their resin bonding applicationsare limited to intracoronal frameworks for natural teeth and dentureacrylic. With the UAS and MUAS designs of the present invention, themajority of precision attachments used in implant dentistry can now bemade so that they can be resin bonded. Not only does resin bonding ofattachments to another metal surface provide for very high interfacialbond strength (8-10,000 psi) but it also eliminates may of the stepsinvolved in casting and soldering as well as the associated problems oftemperature stresses which can affect the physical properties of theattachments.

In order to resin bond the patrix components into detachable framework,they must be designed either with tails that project from the back endof the attachment or the walls of the patrix must be slotted and knurledto provide for an adequately retentive surface. The same design conceptmust also be incorporated into the matrix housing in order to bond itinto the abutment cavity. Furthermore, for those attachments that can beused in conjunction with the UAS system, an entire series of oversizedceramic spacers must be created to make adequate room for the silanecoupling agent if necessary and the resin. Furthermore, becauseduplicating and/or refractoring models are required for this type ofwork, precision attachment matrix and patrix analogs must also becreated. These analogs help to align, repair, fabricate and prevent wearand tear on the precision attachment components. The analogs are usuallymade of brass and can therefore be disposed of far more in expensively.As was discussed in Section VI, only the outer surface of these analogswhich is resin bonded is oversized—the inner mechanically interlockingsurface is an exact likeness of the matrix and patrix components.

The following attachments have been designed with those features inmind.

The Stress Broken Attachment.

The UARS stress broken attachment 84, as shown in FIG. 30A, can beincorporated into the precision attachment stress broken denture. Itspatrix component 88 is designed to be resin bonded into the frameworkand the matrix 86 is designed so that is can be bonded into the acrylicfree end saddle. The following design features give this attachment aunique and specific function—that of stressbreaking.

(a) The patrix component 88 is slotted on both sides of its housing soit can grab onto the resin on the abutment cavity to which it is bonded.The patrix is mounted so that its male extension (guide rail) 90 is theonly portion of the patrix that sticks out beyond the contour of theabutment 22 and the overlying crown 26.

(b) A ceramic spacer comes with the attachment so that the patrixcomponent 88 has a preformed cavity 68 to fit into after the UASAbutment 22 has been cast.

(c) Matrix and patrix analogs are also provided so that when aduplicating model is used the actual precision attachment components donot have to be placed until the prosthesis is taken to the patient'smouth.

(d) The guide rail 90 protrudes essentially vertically from thebackplate 92 of patrix component 88. Incorporated into the guide raildesign is a generally vertically oriented spring 94 for exerting upwardforce on the interior of the matrix component 86, a spacer and anelongated hole 96 for a threaded latch pin 98. The guide rail 90 slopesgently towards the gingiva and its corner is rounded off which allowsthe spring 94 interface to rotate anterior-posteriorally. The guiderail's roundness also allows the attachment 84 to hinge internally andaway from the occlusal surface which further allows the matrix 86component of the attachment 84 to be covered over with resin. Theelongated hole 96 for the threaded latch pin 94 allows the matrixcomponent 86 to move during vertical translation. The guide rail 90 isalso designed so that it is sufficiently long occluso-gingivally toprovide adequate lateral stability; it can even be taperedoccluso-gingivally to allow for con rotational movement. This helpsdramatically reduce the lateral forces of occlusion that are so damagingwith normally designed attachments.

The spacer which fits overtop of the rounded portion of the guide rail90 is used during the assembly and insertion of the attachment 84 toprovide stability and prevent vertical translation. This allows foraccurate occlusal adjustment and equilibration. The spacer features twosmall notches to help stabilize it and hold it in position.

(e) The matrix component 86 has a knurled tail 100 that projectsbackwards from the housing to help provide retention and stability inthe acrylic of the free end saddle.

(f) The matrix component 86 is also designed with an internally recessedand rounded area to receive the spring 94 and the guide rail 90, whichprovides a good footing for the spring-loaded pin 94 and lendsstability. The matrix component 86 fits overtop of the patrix 88 and isheld in place by the threaded lingual latch pin 98.

The Vertex Attachment.

The Vertex attachment 102 according to the present invention, which isshown in FIGS. 31 and 32, features a male component 104 that includes(1) a protrusion 106 that may be generally H-shaped in cross section andthat is adapted to be received in a prosthesis and (2) a generallycylindrical patrix component 108 aligned with the protrusion 106 whoselower portions 110 are generally cone shaped and comprise at least twoleaflets 112 which may be spread apart by insertion of a spreader screw114 into the bore 116 of the component 108. The patrix component 108 isreceived by a corresponding matrix component 118 which is adapted to becast or otherwise formed into an abutment 22 according to the presentinvention and which features a cavity 120 corresponding in shape to theexterior of the patrix component 108 so that spreading of the leaflets112 of the patrix component 108 allows it to be retained in the matrixcomponent 118.

This attachment includes at least 3 functions:

1. A rigidly locking precision attachment;

2. A separable slide attachment (non locking); and

3. A frictional slide attachment with an occlusal adjustment screw toadjust the retention.

The Vertex attachment functions as a rigidly locking attachment when itsocclusal spreader screw 114 is fully engaged to separate the twoleaflets 112. This firmly engages a dimple 122 in the matrix 118 andlocks the matrix 118 and patrix 108 components together. Such anattachment could be used to anchor a telescoped or sectional bridgetogether.

If the posterior most anchor (abutment) of the bridge fails and apartial denture needs to be constructed, the same attachment could beused—all that would be required is a modification to the occlusalspreader screw 114. By cutting its smooth tip portion off, the functionchanges. The Vertex attachment can now be placed and removed withoutever locking together. This would allow the attachment to function in aremovable partial denture. It would still have adjustable retention butmanual manipulation of the leaflets 112 without a spreader screw 114 inplace puts them at risk of loosening too quickly and even breaking.

Instead of cutting off the smooth tip of the occlusal spreader screw114, plastic or metal washers can be simply inserted to bottom outagainst the screw 114. This means that the more washers that are placedthe less the screw tip can engage and spread the leaflets, which resultsin less fractional retention between the matrix 118 and patrix 108. Byremoving a washer, the screw 114 can be tightened further into thechamber and thus the screw tip can engage and spread the leaflets 112further. This results in increased retention. This ability to adjust theretention of the Vertex comes from an occlusal direction and is a muchmore accurate screw adjustment than manual adjustment of the leaflets.

This improved fractional adjustment modification is what gives thisattachment its third function, and in this capacity it is designed to beused in a full/partial arch patient removable crown and bridgeprosthesis which may or may not be implant supported. In eithersituation the matrix 118 is resin bonded into the abutment 22 and thepatrix 108 resin bonded in the metal framework so that the occlusalspreader screw 114 is exposed. The telescopic crowns 26 or sections ofcrowns that fit over top of this framework are screw retrievable so asto allow access to the attachment for micro fine adjustments inretention of the patient removable prosthesis.

The taper of the leaflets 112 is also important to note and can bemodified in any number of ways. It simply allows for easier positioningand insertion of the attachments and overlying prosthesis.

Section IX: Peri Implantitis Prosthetic Design and Surgical Technique:Reevaluating The Causative Factors In Implant Loss And Examining A NewModel Of Osseointegration Failure

Over the last few years, many opinions have been formed regarding whichcausative factors influence dental implant loss. Although it seemsglaringly obvious to some that it is more of a multivalent problem,certain schools of thought still maintain a contrary viewpoint. Forexample, Zarb and Albrechtsson have adopted the “No PeriodontalLigament/No Periodontal Disease” mindset and they believe that“latrogenically induced soft tissue problems are not causes of implantfailure . . . they are just a nuisance—no more, no less.” G. Zarb, etal., Osseointegration: A Requiem for the Periodontal Ligament?, 11 Int'lJ. of Periodontics and Restorative Dentistry 88-91 (No. 2, 1991). Zarband Albrechtsson also believe that a soft tissue seal around the implantis not important and “that applying traditionalprosthodontic-periodontic criteria as contributing factors to theprocess of implant lose is not particularly enlightened thinking.” Id.In fact, they believe that conventional periodontal parameters are notapplicable to the implant peri mucosal environment and should thereforebe regarded as “inconsequential.” For this reason, Zarb and Albrechtssonstate that “there is no need for a measure of mucosal health” instudying implant success rates, even though they admit that “theimmunohistologic profiles of peri implant lesions associated withosseointegration failure still need to be determined and that themechanisms of implants failure . . . are inadequately understood.” Id.

In a recent oral Care Report by D. Braden Stauts, he referred to thecriteria used by Zarb in the placement of single tooth implants. One ofthese criteria was the absence of any significant endodontic orperiodontal problems generally and particularly in the teeth adjacent tothe implant site. Zarb also has been quoted as saying “no periodontalligament, no periodontal disease.” If this last statement is true, whythen would he be concerned about adjacent perio problems, especiallywhen according to him periodontal inflammation is inconsequential? Zarband Albrechtsson contend that the role of micro- and macrotrauma orocclusal stress appears to be the major candidate in the loss ofosseointegration.

At the other extreme is a large group of clinicians and researchers whobelieve perio implant disease is consequential, even though according toZarb they cannot identify the nature of osseointegration failure, whichprovides all the more reason not to adopt such a narrowed field offocus.

Clinicians such as Meffert believe that: (1) without a peri mucosalseal, an apical migration of epithelium into the implant bone interfacetakes place, as well as a fibrous encapsulation of the implant; and (2)occlusal stress or “retrograde peri implantitis” is also a causativefactor in implant loss. R. M. Neffert, What is Peri-Implantitis and HowDo We Prevent and Treat It?, 4 J. Michigan Dental Assoc. 32-33, 36-39(No. 44, 1992).

Still, there are other factors that are not addressed by any of theseclinicians, and until irrefutable scientific data has been compiled toprove otherwise, it would be unwise to adopt any of their positions.This is precisely why the following model of implant failure is offeredand we should be constantly reminding ourselves that implant loss is amultivalent problem. In other words, if one does not completelyunderstand what causes the problem, how can one selectively eliminateany of the pieces of the puzzle?

We must also remember that even though the implant-bone interface is adistinctly different environment than that of a naturaltooth-periodontal ligament, the body still has the sameimmunohistological components (mast cells, lymphotoxins, macrophages,etc.) and the same host defense mechanisms. Therefore, the end resultmay be different with an implant as opposed to a tooth, but the body'sresponse in the same area (the mouth) will always be the same.

Consider more closely what sort of effect flapping the periosteum atstage II uncovery causes on implant failure, and, furthermore, whateffect premature bone loading has on osseointegration.

It is fact that the exposure of bone to our oxygenated surroundingscauses bone necrosis, no matter how insignificant some people may haveus believe it is. Furthermore, the jaw bone derives 30% of its arterialblood supply and 100% of its venous blood supply from the periosteum.Unless the periosteum has completely healed before the implant-boneinterface is loaded, a stress on the system may be the result. Thisstress usually shows up as bone loss. It is the opinion of the inventorthat the cupping around so many of the implants is due to prematureloading as the bone around the implant still does not have adequateblood supply, simply because the periosteum has not completelyreattached. Therefore, as stresses are applied to the implant-boneinterface, instead of absorbing these stresses the bone begins toundergo cortical cratering and a vascular necrosis, resulting in boneloss.

Furthermore, limitations in prosthetic design can also be directly tiedto implant loss because excessive cantilevering forces can createocclusal overloading, which can lead to intrusion and extrusion of theimplants and their ultimate failure. Impassive fitting frameworks canalso have the same effect, as damaging lateral stresses can lead toretrograde peri implantitis. Perhaps the most obvious example of howlimitations in prosthetic design can lead to implant loss is theovercontoured ridge lapped prosthesis, which invariably creates limitedhygienic access. The inability to maintain the surrounding soft tissueproperly leads to inflammation and the eventual breakdown of thehemidesmosomal attachment, which allows for an even deeper penetrationof the inflammatory process. The end result is bone destruction andeventual implant loss.

It therefore behooves us not only to redesign the implant prostheses bymaking them more patient-removable, but also to help eliminate problemsof occlusal overload and damaging lateral stresses by developingstress-breaking techniques. creating non-invasive techniques such as thetapered gingivectomy procedure will also help prevent cupping and lossof peri implant bone. Incorporating split frame techniques and new meansof progressive bone loading will also give the implant-bone interfacemore adequate time to mature.

It is, therefore, not enough to identify all of the causative factors inimplant loss; we must also employ workable solutions such as those ofthe present invention.

Section X: Marking Blade Implants Compatible with UAS and MUAS

There are still many instances where the use of a Modern 2 stage BladeImplant could be considered the treatment of choice when restoring anedentulous space. Even though it is always preferable to join a bladeimplant to either a root form implant or a natural tooth, blade implantscan be indispensable in a situation when a short ridge is characterizedby insufficient ridge width. In such a situation, a root form endosseousimplant would potentially require onlay grafting. The blade implant onthe other hand can alleviate the necessity for grafting or augmentationin one simple and low cost procedure.

The posterior mandible and the chronically edentulous maxilla are bothareas where blade implants can frequently be used. Even though less than10% of all endosseous implants placed are blade form, this still amountsto some fairly substantial numbers (50-60,000 units in North Americaalone).

For this simple reason the inventor believes that all blade implantsshould be modified slightly to allow them to be compatible with the UASand MUAS, as shown, for example, in FIGS. 37 and 38. The modificationsof the 2nd stage of the blade implant 130 are so minor and yet sosignificant. For example, by modifying the threaded heads 132 of theblade and placing a notch 134 into the buccal and lingual aspect of thehead, you do not alter the fit of their standard screw down abutment.However, if you wish to screw down a UAS Core 18 component and lock inits rotational position, you need one or the other of these notches forthe ALS mechanism to engage. Therefore, without the notches, the bladesare not compatible. With these notches they are.

The notches are placed buccal and lingually because the second stagecomponent of the blade is not adjustable and cannot be rotated.Therefore, the notches must be positioned so they do not interfere withthe formation of customized abutment cavities etc. Once the UAS Core hasbeen customized, there is no need to use telescopic copings or cementthe overlying bridgework. Unlike the standard crown and bridge postswhich cannot maintain an exact rotation position or be modified toincorporate intra abutment precision attachments, the components of theexisting technology can.

A recent article by Dr. B. Nicolucci states that “the crown and bridgeposts were placed on the threaded heads of the blades . . . they can becut down to receive copings for draw.” B. Nicolucci, Dental Implants:The Blade Implant, 83 Oral Health 55-60 (No. 9, 1993). The articlefurther states that “the neck of the mesial head of the blade can beseen which allows for easy cleaning and maintenance.” Id. Not only doesthe blade have to be left exposed to ensure cleansibility but it is thisinventor's opinion that unless the prosthesis can be made patientremovable, it is unlikely that it can be readily cleaned particularly itif is fully contoured.

These significant differences and modifications offered by thetechnology of the present invention allow for patient removability,passive fit, better aesthetics and in situations where the blade implantis tied to natural teeth, they allow for the incorporation of resilientcore components into the blade implant. This is something that has neverbeen accomplished up until now, but with UAS and MUAS technology, theseare fairly simple modifications.

Section XI: Modifying the Ankylos Implant System

In order to modify the Ankylos Implant System so that it is compatiblewith the technology of the present invention, modifications must be madeto the Ankylos Implant, the entire abutment system and the threaded basecomponent of the UAS and MUAS. By modifying these components, theimplant itself not only gains a reproducible rotational lock but the 20different prefabricated Ankylos abutments can be replaced with a simplefour piece abutment which can be completely customized to any shape orangulation. This can be done using standard investment castingtechniques or newly developed CAD/CAM procedures. The modifications tothe base allow it to adapt to the mechanical interlock of the implant sothat once the core component has been securely fastened, you have asystem with no central access bore. These modifications also allow forincorporation of resilient components as well as offer all the otherbenefits of the UAS and MUAS.

The Ankylos Implant System has a conically tapered recess and reliesupon a temperature gradient to cause expansion and subsequent frictionalretention between two dissimilar metal surfaces. It does not utilize amechanical interlock for rotational stability. This is achieved byfabricating an overlying telescopic framework.

The limitions of this approach are as follows:

(1) If the abutment ever has to be removed or comes loose, exactrotational repositioning is extremely difficult if not impossible.

(2). These Ankylos abutments are still screw retained and have centralaccess bores.

(3) One and two together preclude the use of intra abutment precisionattachment patient removable prostheses and also bring to mind concernsover screw loosening and passive fit etc.

(4) The extra steps involved in fabricating telescopic copings requiredto establish rotational stability is time consuming, costly and createsextra bulk.

(5) There is no means of developing an individual anatomically contouredgingival cuff using the prefabricated “sulkusformers.”

(6) The system is limited to using prefabricated angulated abutmentswhich cannot incorporate resilient components.

(7) If the metal expansion of the abutment relies on memory metalcontent (nickel, vanadium, etc.) FDA approval in U.S. will beexceedingly difficult to achieve due to a concern over allergicreaction, corrosion and biocompatibility.

(8) Finally, the components are specific to the Ankylos system. The arenot interchangeable or compatible with any other implant system whichdefinitely limits this product's market.

Basically, the Ankylos system has the same old problems as all the otherconventional systems and until something is done to correct this, theAnkylos system will be competing on a level playing field with all therest of its competitors.

By making following modification all of these problems can beeliminated:

(1) Create concentric slots or ribs in the tapered portion of theimplant and a machined threaded UAS base to mate with it so that the UASthreaded base can be held in a multiple number of mechanicallyinterlocking exact rotational positions.

(2) This same type of multiple rotational positioning can be achieved bymachining a UAS threaded base with radial ribs to engage the fourpreexisting notches on the superior edge of the implant. Either of thesemethods will allow the UAS threaded base to be positioned in a varietyof exact rotational position without using a memory metal or temperatureexpansion. This also means that when the UAS core is screwed down, ittoo will have reproducible rotational positions and therefore, so willthe customized abutment (including a customized transmucosal cuff) andthe intra abutment precision attachments. This can all be achievedwithout telescopic copings.

These small but distinct modifications mean that the in Ankylos Systemcan be easily made compatible with the UAS and MUAS. This allows formore system flexibility, such as incorporation of Resilient Cores andnew prosthetic designs.

What in claimed is:
 1. A dental implant abutment assembly, comprising:a. an implant for embedding in the osseous structure of a patient; b. atransition structure connected to said implant, said transitionstructure including a distal portion located distally of said transitionstructure relative to a central axis of said transition structure, and aproximal portion located proximally of said transition structurerelative to a central axis of said transition structure, said transitionstructure containing a surface discontinuity for receiving a distal endof a transverse fastener; c. a core structure connected to saidtransition structure, said core structure including a distal portion anda proximal portion and an interior surface and an exterior surface, saidinterior surface generally forming a concavity in said proximal portionof said core structure, said interior surface adapted in shape toreceive said distal portion of said transition structure, said corestructure containing a bore oriented substantially transverse to saidcentral axis of said transition structure; d. a transverse fastenerthreadably received in said transverse bore, said transverse fastenersecuring said core structure to said transition structure; e. asurfacing structure connected to said core structure; f. wherein saidsurfacing structure and said core structure contain no central boreoriented substantially parallel to said central axis of said transitionstructure, and said core structure is connected to said transitionstructure nonrotatably.
 2. A dental implant abutment assembly accordingto claim 1 wherein said implant includes an interior threaded bore andsaid transition structure includes a threaded surface adapted to bethreadably received in said implant threaded bore for connection of saidtransition structure to said implant.
 3. A dental implant abutmentassembly according to claim 2 wherein said transverse bore in said corestructure is threaded and said transverse fastener comprises a screwthreadably received in said threaded transverse bore.
 4. A dentalimplant abutment assembly according to claim 1 wherein said transversefastener in said core structure impinges on a surface of saiddiscontinuity in said transition structure, said fastener precludingsaid core structure from inadvertent separation distally from saidtransition structure.
 5. A dental implant abutment assembly according toclaim 1 wherein said exterior surface of said transition structureincludes a threaded surface, said interior surface of said corestructure includes a threaded surface, and said threaded surface of saidcore structure is secured to said threaded surface of said transitionstructure, said threaded surfaces precluding said core structure frominadvertent separation distally from said transition structure.
 6. Adental implant abutment assembly according to claim 1 wherein said corestructure comprises an interior element and an exterior element, saidinterior element generally forming said proximal portion and saidinterior surface of said core structure, said exterior element generallyforming said distal portion and said exterior surface of said corestructure, said exterior element cast to said interior element.
 7. Adental implant abutment assembly according to claim 6 wherein saidtransverse bore penetrates said interior element and said exteriorelement of said core structure.
 8. A dental implant abutment assemblyaccording to claim 1 wherein said core structure is formed of a singlemetallic element, an exterior surface of said single metallic elementmachined generally to form said distal portion and said exterior surfaceof said core structure, said distal portion and said exterior surface ofsaid core formed of a shape generally to receive said surface structure,said surface structure in combination with said core structure generallyforming a human tooth in shape.
 9. A dental implant abutment assemblyaccording to claim 1 wherein a screw mounted substantially transverse tosaid central axis of said transition structure connects said surfacestructure to said core structure.
 10. A dental implant abutment assemblyaccording to claim 1 wherein said implant is a non-blade implant.
 11. Adental implant abutment assembly according to claim 10 wherein saidimplant is a root form implant.
 12. A dental implant abutment assemblyaccording to claim 10 wherein said implant is a sub-periosteal implant.13. A dental implant abutment assembly according to claim 1 wherein saidimplant is a blade implant.
 14. A dental implant abutment assemblyaccording to claim 1 wherein said surface structure is a porcelainlayer.
 15. A dental implant abutment assembly according to claim 1wherein said surface structure is a crown.
 16. A dental implant abutmentassembly according to claim 1 wherein said surface structure forms partof a denture.
 17. A dental implant abutment assembly according to claim1 wherein said surface structure forms part of a prosthesis.
 18. Adental implant abutment assembly comprising: a. an implant adapted to beembedded in the osseous structure of a patient, said implant containinga central axis oriented substantially longitudinally of said implant,said implant including a threaded bore formed in a distal portion ofsaid implant; b. a fixation element including a proximal portion whichincludes a threaded surface, said threaded surface threadably receivedin said threaded bore of said implant whereby said fixation element iscoupled to said implant, said fixation element including a distalportion adapted in shape to couple to and retain a base element; c. abase element comprising at least one surface adapted to couple to and beretained by said distal portion of said fixation element whereby saidbase element is precluded from inadvertent separation from saidtransition element, said base element including an exterior surfacecontaining a surface discontinuity for receiving a transverse fastener;d. a core structure connected to said base element, said core structureincluding a distal portion and a proximal portion and an interiorsurface and an exterior surface, said interior surface generally forminga concavity in said proximal portion of said core structure, saidinterior surface adapted in shape to receive a portion of said baseelement, said core structure containing a bore oriented substantiallytransverse to said central axis of said implant; e. a transversefastener threadably received in said transverse bore, said transversefastener securing said core structure to said base element; e. a surfacestructure connected to said core structure, said surface structureformed generally in the shape of a tooth; f. wherein said surfacestructure and said core structure contain no central bore orientedsubstantially parallel to said central axis of said implant.
 19. Adental implant abutment assembly according to claim 18 wherein saidtransverse fastener in said core structure impinges on a surface of saiddiscontinuity in said base element, said fastener precluding said corestructure from inadvertent separation distally from said base element.20. A dental implant abutment assembly according to claim 19 whereinsaid transverse bore in said core structure is threaded and saidtransverse fastener comprises a screw threadably received in saidthreaded transverse bore.
 21. A dental implant abutment assemblyaccording to claim 18 wherein said fixation element and said baseelement are coupled to form a unit and said core structure is couplednonrotatably to said unit.
 22. A dental implant abutment assemblyaccording to claim 18 wherein said exterior surface of said base elementincludes a threaded surface, said interior surface of said corestructure includes a threaded surface, and said threaded surface of saidcore structure is secured to said threaded surface of said base element,said threaded surfaces precluding said core structure from inadvertentseparation distally from said base element.
 23. A dental implantabutment assembly according to claim 18 wherein said core structurecomprises an interior element and an exterior element, said interiorelement generally forming said proximal portion and interior surface ofsaid core structure, said exterior element generally forming said distalportion and said exterior surface of said core structure, said exteriorelement cast to said interior element.
 24. A dental implant abutmentassembly according to claim 23 wherein said transverse bore penetratessaid interior element and said exterior element of said core structure.25. A dental implant abutment assembly according to claim 18 whereinsaid core structure is formed of a single metallic element, an exteriorsurface of said single metallic element machined generally to form saiddistal portion and said exterior surface of said core structure, saiddistal portion and said exterior surface of said core formed of a shapegenerally to receive said surface structure, said surface structureincluding a porcelain layer generally forming a human tooth in shape.26. A dental implant abutment assembly according to claim 18 wherein ascrew mounted substantially transverse to said central axis of saidimplant connects said surface structure to said core structure.
 27. Adental implant abutment assembly according to claim 18 wherein saidsurface structure is a porcelain layer.
 28. A dental implant abutmentassembly according to claim 18 wherein said surface structure is acrown.
 29. A dental implant abutment assembly according to claim 18wherein said surface structure forms part of a denture.
 30. A dentalimplant abutment assembly according to claim 18 wherein said surfacestructure forms part of a prosthesis.
 31. A process for forming a dentalimplant abutment assembly, comprising: a. embedding an implant in theosseous structure of a patient, said implant including a central axislongitudinally to said implant; b. providing an abutment structure andconnecting said abutment structure to said implant; c. providing a coreblank, said core blank including an interior surface adapted to receiveat least a portion of said abutment structure, said core blank includinga substantially transverse bore adapted to receive a fastener; d.machining the core blank to form a core of a predetermined shape whichcorresponds more closely to at least some contours of a human tooth thansaid core before machining; e. connecting said core to said abutmentstructure using no fastener which penetrates said core substantiallyparallel to said central axis of said implant; f. installing saidfastener to preclude said core and said abutment structure from rotatingrelative to each other, and to preclude said core from inadvertentseparation from said abutment structure; and g. placing a surfacestructure on said core to form a shape substantially conforming to ahuman tooth.
 32. A process according to claim 31 in which the machiningis performed by a computer controlled process.
 33. A process accordingto claim 31 in which the machining is performed using imaging renderedon a computer.